Make record button primary when set to record only

When the user has set the mode to "record to file only", make it so
that the "Start/Stop Recording" button is enabled, and that the
"Start/Stop Streaming" button is disabled.  Having both buttons
enabled when in 'record only' mode is just a bit confusing.
Merge branch 'master' of https://github.com/jp9000/OBS
Fixed divide by 0 in frame drop percentage calculation
Allow settings dialogs to cancel applying settings
Allow disabling QSV/NVENC even if no hardware support is detected

Also make checkboxes semi-exclusive, pending further refactoring into
a select box or similar gui element
Refactored encoder initialization, display errors instead of silently using x264

Added a bunch of (localized) error messages for QSV and NVENC