Blender Git Loki

Animation: Make dopesheet filter labels consistent

There are three different label styles for the three Dopesheet filter
labels:

- "Display Hidden", which uses "Display" rather than "Show" as the other
two options.
- "Show Errors", which does not use the word "only" to indicate it will
hide all the non-error channels.
- "Only Selected", so no "show" or "display" in the label at all.

This commit changes:
- Always use the word "Show", not "Display".
- Always use the word "Only" when enabling the filter hides everything
else.

Reviewed By: billreynish

Differential Revision: https://developer.blender.org/D7742