skin engine: New logical 'and' and 'or' tags to evaluate multiple tags in a single conditional.

Use these tags to stop having multiple conditionals.. e.g:
OLD: %?C<%?Ia<something>>
NEW: %?and(%C, %Ia)<something>

Change-Id: Ia3bbe4611cf808e87dcd1b1147181461fa08294a
6 files changed