demos: Restrict `opacity` to non-flagged icons only
demos: Restrict `opacity` to non-flagged icons only

Also make opacity follow base text color.

Change-Id: I60532da11bcb52de314dc7f750c192839b0f31f6

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui