Several more improvements importing FB projects

- Parsing of directory variables.
- Better detection of the external themes path.
- Support for custom themes with non-standard names.
- Support for SDK themes.
- Support for packaged sourced paths.
- Support for packaged libraries.
- Force the current working directory to the imported project directory
to solve problems with relative paths.
Fix MySQL spelling
Haxe C++ template: fix Run.bat always running the -debug version
Macro -> Execute Script: don't error when open file dialog is cancelled
Merge pull request #477 from Gama11/MacroExecuteScript

Macro -> Execute Script: don't error when open file dialog is cancelled
Merge pull request #474 from Gama11/HaxeCppTemplate

Haxe C++ template: fix Run.bat always running the -debug version
Merge pull request #473 from Gama11/patch-2

Fix MySQL spelling
Merge pull request #453 from Neverbirth/airimprovements

Several more improvements importing FB projects