If failing to import file content data, drop contents imported thus far

This patch adds an export+import method to the file command line module. The
file export is agnostic of the file storage backend. It writes the files
with the %file record data to standard-out or to the file given by the -f
option. The file is a considered a stream and can quietly be compressed and
can be read back in as a stream (no seeking is performed in the import
process).

This patch also makes a slight edit to mPDF to allow better detection of
substitions in characters, as the DejaVu fonts shipped do not support Thai
glyphs.

And allow for @context to add context to the bare string literal. For
instance,

    /* @trans, @context "noun" */ 'Open'

Would mark the string 'Open' translatable with context "noun".

And add translations for the draft mechanism

Also add some logic to the POT builder to warn about incorrect arguments to
the __() function and friends as well as warn about _() usage.

The software defines at least three contexts for the phrase "Open"

  * The name of a ticket queue (Open tickets)
  * A status of a ticket (Open / Closed)
  * An action to be performed (Open a ticket)

References:
(Crowdin login required)
http://i18n.osticket.com/translate/osticket-official/148/enus-de#2915

Also, the final version of the system will not require the `gettext`
extension for PHP

Also add several lint fixes for packaging