Proof tree view: Multiple small changes for readability #3012

I've digged these changes up from my main branch from over a year ago and made them cleaner.

• Cleanup some of the code
• Speed up ProofTreeSearchBar by caching the search strings (Makes a huge difference for large proofs)
• Fix example dialog loading previously hidden example on double-click on a folder

Elide long rule app names and move them to the tooltip

Normalize whitespace in rule names

After:

Before:

Move applied on term of OSS nodes to the tooltip

After:

Before: