Fixed issue with regex not properly handling dot in file names without extensions
Expanded regex to check for valid file extensions
Exposed getFilenameWithoutExtension

Also added appropriate comments to explain why we need to remove the
file extension when the filename is used as the name of the theme
Cleaned private jsdoc annotation and a few grammatical mistakes
Adding ability to remove ".min" from filename
Merge pull request #8677 from MiguelCastillo/fonts-filename

Fixes handling of CSS file name to theme name