win-wasapi:  Use macros instead of strings

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.
Use uint8_t* instead of void* for texture data

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.
libobs:  Fill in rest of 'path' property code

A path should have a filter, default search directory, and a way to
indicate whether or not a directory or file is desired.
Implement 'path' property in to properties view
Add FFmpeg image file support to the core
Add MagickCore image file support to the core

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.
Add image source plugin

A simple plugin that does nothing more than display an image file as a
source.
Add image source module to obs-studio basic UI

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