Adding condition for skipping symlinks when installing extensions via the extension manager

When installing extensions that have symlinks via the extension
manager, they will fail with a message regarding an invalid zip file.
This can be tested with
https://github.com/MiguelCastillo/Brackets-SymbolicLinks
added pointer-events to CSS Code Hints
Add css property filter in CSSCodeHints/CSSProperties.json
Merge branch 'master' into MiguelCastillo-master
Adds a test for files with symlinks
Merge branch 'MiguelCastillo-master' (PR #5919)
Merge pull request #6159 from telis93/filter-property-add

Add css property filter in CSSCodeHints/CSSProperties.json
Merge pull request #6156 from calweb/pointer-events-codehint

added pointer-events to CSS Code Hints
alphabetized CSS pointer-events properties
Merge pull request #6179 from calweb/pointer-events-codehint

alphabetized CSS pointer-events properties