CI: Linux - Install libfdk-aac-dev

Closes jp9000/obs-studio#840

UI: Fix segfault when no system tray exists

image-source: Move file modification check before animation processing

Bug introduced in jp9000/obs-studio#861

Closes jp9000/obs-studio#860

Allows copying filters from one source to another.

Closes jp9000/obs-studio#860

UI: Add workaround to fix deleting final scene bug

The "default" preset is not an actual default, but something Nvidia
decided to just call that way.  It yields the worst quality per bitrate
out of all the presets, for no actual benefits.  The actual FFmpeg
default is the hq one, which yields the best quality, especially when
twopass mode is enabled.

I can't think of a way to keep the "default" preset in a non-confusing
way, and as it gives no known benefits, might as well just remove it
entirely.

(Jim edit: Also made it so that if the settings have it set to
"default", it automatically treats it as "hq")

Closes jp9000/obs-studio#865

CI: Linux - Install FFmpeg from source

[skip appveyor]

rtmp-services: Update maximum bitrate for Twitch

Updated max 3.5 to 6. See https://help.twitch.tv/customer/portal/articles/1253460-broadcast-requirements#Broadcast%20Requirements

rtmp-services: Update ingest list for Restream.io

The code to process GIF animations contains a return statement that
skiped the file modification check, if the source is not in an active
scene. Like that images in the preview scene of studio mode would never
update, when they get modified on disk.

Also reloading the image, if an animation file has been modified before
processing the old animation that will be replaced later anyway, seems
like a better way to do it.

[skip appveyor]

Same issue as 77ceb97f corrected but for POST responses.

CI: Use ccache to speed up the build

Speeds up recompilation by caching previous compilations and detecting
when the same compilation is being done again. [skip appveyor]

This would cause people to download the 64bit files when they were on
the 32bit version of windows, even though those files aren't meant to be
installed.

The file could deflate infinitely until hard drive space ran out.

The updater would return HTTP 400 on an empty json array upload for the
patch manifest.

The GetTempPath and GetTempFileName functions weren't being used
correctly, GetTempFileName always create a temporary file, and was
creating a temporary file in the root directory of the hard drive
unintentionally.

EnumProcessModules may not work correctly cross-arch, so use
GetProcessImageFileName instead to ensure no issues in that case.

Used by the update module on windows.

To check to see if a file is locked, it must be opened for writing, not
reading.

CI: OSX - enable sparkle

CI: OSX - Brew install speexdsp