[sancov] Adding covered/uncovered tables to coverage report.

Summary:
This change adds 3 tables to html report:
- list of covered files with number of functions covered.
- list of not covered files
- list of not covered functions.

I tried to put most coverage-calculating functionality into
SourceCoverageData.

Differential Revision: http://reviews.llvm.org/D17421

llvm-svn: 261287