Allow icon type properties to be filterable

Props nyoz
Overload __get() method in Menu_Icons_Type
Set Font Awesome version to 4.1.0
Use instanceof instead of is_a()
Fix input style on settings sidebar
Remove duplicate Dashicons share icon
Foundation Icons 3.0
Merge pull request #29 from kucrut/foundation-icons

Foundation Icons 3.0
Add info about Jetpack's Custom CSS module in FAQ
Change "Select icon" to "Select" for cosistency
Add "Extensions" tab to settings meta box
Update changelog
Add FAQ entry about filtering icon type properties
Bump version to 0.5.0
Add new Dashicons icons
Regenerate readme for GitHub