Count warnings per project and dump out CSV format.

* No change to html output, except removing unused "PageTop" anchor.
* Add --gencsv flag to output a CSV file instead of html file.
  CSV files are combined to a table for dashboard charts.
* Count warnings from selected source project directories.
* CSV output lines are:
   num_of_warnings,project_name,warning_description
* project_name is empty for sum of warnings from all projects.
* warning_description could be:
  (1) "<severity>: <warning type description>"
      for one warning type, or
  (2) "<severity> warnings"
      for all warning types of the severity.

Change-Id: I1cf976ed0cf142091226b22665b7f28d383608fd
Test: run through current build.log files.