Correctly strip the separator character when loading plain-text files
Send a fake focus lost event to wxSpinCtrlDouble before reading the value

wxSpinCtrlDouble only updates its value when the spin button is clicked
or it loses focus, and in some cases we want to read the value while it
still has focus.

Closes #1610.
Only generate fake focus lost events when using the generic implementation
Fix issues with loading the video AR from subtitles

Removing the first character from the non-custom case resulted in an
error when the value was empty and resulted in nothing happening when a
valid value was present.
Clean up signal.h a little
Use unique_ptr in Connection rather than a shared_ptr
Redesign VideoFrame

Eliminate the manual memory management and shuffle around where the
copies are made to eliminate the need for non-owning video frames.
Fix the Select None button in the export dialog
Use gil in ColourButton rather than wxMemoryDC

Basic drawing with wxMemoryDC is relatively slow.
Slightly simplify spectrum image generation in the colorpicker
Bump dependency versions
Retry commits of file writes for up to a second to work around AV scanning

Poorly-written antivirus software briefly lock newly written files to
scan them for viruses, which makes the rename from the temp file to
actual file fail. Work around this by retrying the rename up to ten
times.

Closes #1620.
Eliminate double dot in temporary file names

Probably didn't cause any problems, but it was slightly ugly.