Bug 696515

The publican-push/po-push commands have separate options to specify the directories which contain POT and PO files.

But in most cases, especially for publican, the POT directory and the locale directories have the same parent directory, and it should be possible to find the POT and PO dirs from this parent directory.

The defaults are "./pot" and ".", which works well if the pot and locale dirs are directly under the current dir.  But if the pot and locale directories are under a subdirectory, you end up needing a command line like this:
  zanata publican push --srcdir docbook/pot --transdir docbook --import-po

If we were to introduce a --dir option, this would be enough:
  zanata publican push --dir docbook --import-po

This would look for pot files in "docbook/pot", and PO directories in "docbook".

--dir could work in a similar way for publican-pull (basically an alias for --dstdir).

In the case of po-push/po-pull, the rules for finding POT and PO files from a --dir option would be slightly different, but the principle is the same: --dir should point to the parent of the POT and PO dirs, and we should use sensible defaults to find the actual POT/PO dirs.  We should probably discuss the appropriate defaults for software projects.

NB: If present --srcdir, --transdir and --dstdir should override --dir's defaults.