Handle case where file is empty (don't index invalidly).
Re-organise external-facing headers to be more easily used

* renderdoc/api/replay/ contains all the headers for using the replay and
  analysis side of renderdoc (like in a UI or auto-testing tool)
* renderdoc/api/app/ contains the headers if you wanted to write a
  renderdoc-aware application.
Add api for applications aware of renderdoc to get list of captures
Update help text
Improve type display in constant buffer previewer
Set Debug Messages title correctly
CBuffer window is a dialog now, with ability to set custom layout
linux compile fix
Add API to set which keys trigger cap etc in-program

* Not exposed in the UI to be able to configured just yet, but it can be
  set by a program that's renderdoc-aware.
Linux compile fixes
Remove UNorm_SRGB component type as it's redundant
Remove old file no longer in project
Move InitRemoteAccess to app API
bugfixes to CopyTex2DMSToArray and CopyArrayToTex2DMS
In GetTextureData() handle MS textures as if they were arrays

* Client code is expected to handle this and request arrayIdx N for the Nth
  sample (possibly offset if it's an array of MS textures).
Add variants to stb_image_write that take FILE* instead of filename
Move DDS writing code out from d3d11 driver
Move SaveTexture logic to replay layer

* Expand the abilities of the GetTextureData in replay drivers
  to be able to resolve samples and render down to RGBA8 unorm
  for file export to other programs.
* Greatly improve the ability to save textures - in theory any
  texture format/type/dimension/etc should now be mappable in
  sensible & useful ways to output formats.
Add a dialog to guide users to selecting available save options
64bit compile fix