UI: Fix grayed out Copy option in sources context menu

Fixes a bug where the thread local variable "current_lua_script" is not
set when calling script_tick.

(This commit also modifies the frontend-tools module)

Prevents a potential crash when script_log is called by a thread spawned
by a python library.

This fixes a problem introduced in #1050 where the Copy option would
be grayed out when rightclicking a source above the currently selected
source. This also retains the functionality of not having the Copy option
enabled when no source is selected.

CI: Fixes to get OSX packaging working on travis

CI: Fetch RVM gpg key on osx

CI: Fix a ruby issue on travis OSX

CI: Update OSX deps build scripts

CI: Point to newer brew python

Makes it so that the scripting cmake variable ENABLE_SCRIPTING is a user
variable rather than a global internal cmake variable, and defers the
internal global cmake variable to SCRIPTING_ENABLED instead.

Fixing a reference to Rachni theme folder, some minor tweaks and
reverting volume meter foreground colors to original brightness.

Closes jp9000/obs-studio#1169

CI: Install swig and luajit for osx travis

Prevents Python from automatically trying to load from PATH on startup
on windows.  The user should set their Python 3 path themselves.

Prevents the user when detect-amf piped program crashes due to driver
crash.

UI: fix Multiview labels readability

This reverts commit 5cf11d67.

CI: Update CEF version on travis for osx

cmake: Search for Python 3.4

Fixes an issue where Python libraries aren't found on Ubuntu 14.04
because CMake 2.8 only searches up to Python 3.3.