Remove high-level UTIs from Quick Look generator

This should allow Quick Look generators to function when they target a more specific UTI. Discussed in #1141 and #1168.
Re-arrange code
Remove support for extension filtering (Go to File)

This mode probably did more harm than good — instead we’ll introduce a glob match mode activated by using an asterisk in the filter string, which will then be able to achieve the same.
Allow using globs in Go to File

Globs are identified by containing at least one asterisk.
Handle themes with invalid foreground/background color

Fixes #1179
Parse theme colors using 8-bit notation (#RGB)

This is to improve interoperability, as some themes (not produced by TextMate 1.x’s theme editor) use this shorter notation.
Add assertion