cmake support for ImageMagic vs. libavcodec

Compatibility with older FFmpeg versions may be broken if the av_frame_*
functions are used instead of the avcodec_* equivalents.

Implement image file support

...We really need to make this search for modules and automatically load
them.

A simple plugin that does nothing more than display an image file as a
source.

MagickCore is provided here as an alternative to FFmpeg in case FFmpeg
is not easily supported (for example, debian-based linux distros).

NOTE: Cmake configuration needs to be changed in order to allow
MagickCore image support.

A path should have a filter, default search directory, and a way to
indicate whether or not a directory or file is desired.

NOTE: In texture_setimage, I had to move variables to the top of the
scope because microsoft's C compiler will give the legacy C90 error of:
'illegal use of this type as an expression'.

To sum it up, microsoft's C compiler is still utter garbage.

Instead of using strings for setting names, use macros.  Macros prevent
mis-spellings, prevent usage of the wrong name, and if you get it wrong,
it will simply fail to compile, helping to ensure that the right setting
value is being used.

Rename GS_ERROR_MODULENOTFOUND to GS_ERROR_MODULE_NOT_FOUND

Update mac-avcapture to use recent property and data changes

Similar to the shader functions, the effect parameter functions take
the effect as a parameter.  However, the effect parameter is pretty
pointless, because the effect parameter.. parameter stores the effect
pointer interally.

...I'm actually concerned that I went a bit overkill trying to prevent
backwards compatibility issues with this abstraction design, because
this is a large number of files that have to be modified just to add a
single graphics subsystem export.  Someone's going to strangle me, and
when you know that someone might strangle you, that means that you did
something wrong.  We'll have to look in to simplifying this in the
future without killing backward compatibility safety.

Getting cubemaps and volume textures from file is very unlikely to ever
happen for our purposes.

Since adding a source now opens the config dialog for that source
the convenience gain from having a device automatically start capturing
is outweighed by the inconvenience from having captured images
unintentionally recorded/streamed

This requires the (localized) device name to be stored

Configured presets that are unsupported are now preserved in the user config,
but listed as disabled

Update to new module locale API

The module callback obs_module_set_locale will be called after loading
the module, and any time the locale is manually changed via core API.

When this function is called, the module is expected to load new text
lookup values for all the text it uses based upon the current locale.

The locale parameter was a mistake, because it puts extra needless
burden upon the module developer to have to handle this variable for
each and every single callback function.  The parameter is being removed
in favor of a single centralized module callback function that
specifically updates locale information for a module only when needed.

Having the value stored here is somewhat pointless, so this is one step
in fixing the locale handling.  Locale should be handled by the modules
themselves with their own loaded locale lookup information.

This API is used to set the current locale for libobs, which it will set
for all modules when a module is loaded or specifically when the locale
is manually changed.

Previously dstr_move would try to free the uninitialized value in
DStr::str::array