Reduce the total number of calls to getCallsign()

Summary: Ref T4245. Before doing any hard work here, we can dramatically reduce the number of things that make calls to getCallsign() to make navigating things easier. Almost all of them only care about a monogram, URI, or display name.

Test Plan:

• Searched for r uniquename in jump nav.
• Ran bin/repository reparse --change rXXXyyyyy --trace, observed query against bad commit table.
• Ran bin/search index rXXXyyyy --trace --force, observed proper title when indexing commit.
• Browed repository list, saw proper rXXX and appropriate link targets.
• Mentioned rXXX in Remarkup, got a link to the right place.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4245

Differential Revision: https://secure.phabricator.com/D14923