Command to search for projects under a dir and import them.

:ProjectImportDiscover invokes ProjectImport for each dir that
contains a .project file.

Testing:
- Verified that all projects under a dir are imported.
- Verified that message is show when there are no project files.
Merge remote-tracking branch 'rkannan82/master' into import-discover
add docs for ProjectImportDiscover

refs #371