common: Put scopeMatch in util, use in highlights

common: Put scopeMatch in util, use in highlights

Move ignore rule scopeMatch() to util to share usage with highlight
rule scope matching.

Use scopeMatch() in highlight rule channel name processing.

Advantages:
> Simpler to manage common cases
> Shares the same rules as ignore lists, already-learned behavior
Disadvantages:
> No way to escape ';' in rules
> No longer able to use full regular expressions
> Breaks existing channel name rules (also applies to local!)

(Another approach is to keep only local highlight rules inconsistent)