several small ItemDisplay improvements

[BetweenWalls]

• new %CL% keyword (short for "conditional line") which works the same as %NL% except is ignored if it's the first or last part of a name/description
• new %LBRACE% and %RBRACE% keywords for "{" and "}" symbols so they can be used in descriptions
• EQUIPPED now applies to equipped mercenary items too
• Removed extra trailing/leading space from magic items that didn't have both a prefix and suffix
• Removed some leading/trailing blank spaces for text notifications (all of them except for 3 trailing spaces per color keyword)

[BetweenWalls]

Note: I was testing on the old graphics, and just realized that the 3 trailing spaces per color keyword are actually removed when HD text is enabled. The changes I made don't affect that, but I did leave a "TODO" comment in the code saying they still need to be removed - that comment should probably explicitly mention that it only applies for ddraw or non-hd text.

[Canite]

Similarly to the other pull request, I'll look through this when I've got some time.