block main panel when side menu is open

ported fix for pull-request #490 to 2.1 branch

Issue
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See issue #468, main panel is scrollable when side menu is open.

Test Case
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- Open kitchen sink app and toggle side menu, notice that main panel is scrollable.

Fix
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- creates a mask on main panel when side menu is open
- tapping on main panel when side menu is open will close side menu