Use older FFmpeg API functions for AVFrame

Compatibility with older FFmpeg versions may be broken if the av_frame_*
functions are used instead of the avcodec_* equivalents.
Add ImageMagic/Libavcodec find logic
Use propper ffmpeg compatiblity instead of relying on deprecated functions
Add missing header to CMakeLists.txt
Merge pull request #132 from BtbN/cmake_magick

cmake support for ImageMagic vs. libavcodec
Add '.directory' to .gitignore
Fix bug magickcore file loading freeze

This seemed to happen if the 'file' variable was NULL.  For some reason,
magickcore would just totally freeze.
Don't use swscale if format is supported
Set default blend function to srcalpa/invsrcalpha
Use signal/slot when creating a source via popup

I realized that there's no other way to share the menu if I want to add
it as a sub-menu somewhere else.
Give the 'add source' popup the 'Add' title

This allows the popup to be appended directly as an item for other
popups.
Fix renderer listbox to be a global config setting

The current renderer should be a global config setting, not a local
setting.
Add signal for renaming sources
Implement renaming of scenes/sources
Do not rename items if the name is the same
Fix renaming bugs, deny if empty, and simplify

I screwed it up a bit originally, using && instead of ||.

Use 'trimmed' function to prevent sources with leading or trailing
whitespace.

Also, do not allow an empty value.
Implement context menu on 'sources' box