Added FFmpeg recorder support

Screen Recorder tab now has a checkBox: Run CLI afterwards so that you
may execute your favourite Command Line Interface (e.g. x264.exe,
ffmpeg.exe) to encode what has been recorded by ShareX. You may choose
Video for Windows (VfW), FFmpeg or Animated Gif to record your screen.
VfW will allow you to create uncompressed AVI streams or compressed
streams using x264VfW etcc; FFmpeg will allow you to create MPEG4
streams - this is handy if you do not have Administrator access to
install x264VfW to compress your streams. Run CLI afterwards checkBox is
disabled for Animated GIF until we actually see a CLI that could take
GIF and output to a movie file.
Updated Inno Setup to exclude AForge.*.dll files
AVIcache, FFmpegCache, HardDiskCache all inherit ImageCache

AVIcache, FFmpegCache, HardDiskCache all inherit ImageCache
rename Cache cs files
Code improvements for screen recording
Support CLI after creating Animated GIF

Support CLI after creating Animated GIF so that you can still run CLI
for GIF optimizations such as http://www.lcdf.org/gifsicle
Support CLI after creating Animated GIF (proper)
Changelog update
Automatically download and install FFmpeg files
fixed #125

If you copy a URL of an image, you can now upload this image using
Clipboard Upload.
TODO: This could extend to files too.
URL upload changes
Better url file checking
fixed #127: Pushbullet device name null check
Reorgansing files for FFmpeg CLI support
Created FFmpegCLIHelper

ffmpeg.exe quits as soon as it starts!
Modular ScreencastOptions
ExternalCLIManager.cs changes
SwapStdErrAndStdOut support for ffmpeg
ffmpeg cli changes
ffmpeg cli recording works now