Submerge 3.1

- Fixed an annoying bug that could cause a crash when exporting.
- Pick a folder for exported files in Preferences... General.
- Initial support for WebVTT subtitle import (not all features).
- Export presets adjusted once again to produce smaller files faster.
- Subtitle font styles completely revised.
- Added the option to select bold fonts.
- Subtitle shadow and blur radius now properly scaled.
- Quickly select subtitle style and size from the Tools popover.
- New 1080p export presets for Web.
- Welcome window and Quick Start Movie updated.
- Some localization fixes.