Introduce a proper CC type to hold style selection information
Delay signalling of enabled state changes until the op batch is complete

The internal state is reset immediately so any external calls to disabled
features will be correctly disabled. Delaying the signal however ensures
processing of groups of operations remains performant.
Enabled direct text styling only if current selection is a text range

Prevents the controller advertising things such as bold and underline
are valid operations for an inline image (they are not!).
Avoid enabling remove hyperlink button if hyperlinks feature is disabled
Add event subscription tracking object to simplify per-frame subscriptions

A common use-case for UI components is to only update the UI state just
before the next frame is rendered, irrespective of how many times a
signal is fired within a given batch of operations.

The event subscriptions object allows these to be easily created and
tracked, and also makes it easier to ensure all subscriptions are cleaned
up at the end.
Merge pull request #676 from peitschie/dfc-enabled-speedup

Improve large selection removal performance