Set language- and script-specific fonts.

Use Amiri for Arabic and Nafees for Urdu, and Linux Libertine for Latin.

Change-Id: Iad7a8228274a0c33094f66a76d8184ac3e97ee50
Update test cases (use latest bundler; add multi-wiki test).

Change-Id: I07cb5d9abe32d2e2432eb0d36952c3f12f3e0cf5
Ensure that errors inside promises result in non-zero exit status.

In theory the promise infrastructure is supposed to take care of this
for us when we use the .done() method -- but in practice sometimes
exceptions sneak through the cracks.  Do The Right Thing explicitly.

Change-Id: I54d2b92d121a71404ff9fce6b35d62d61ce784ec
Improve Arabic, Devanagari, and Urdu fonts.

Adds fonts-hosny-amiri and fonts-nakula to the list of package dependencies.

Change-Id: I1855302d201b7e9813992e00a207ec2c35020d2d
Improve font/language handling in multiwiki collections.

Ensure that the table of contents is always in the language of the
collection as a whole, even if individual articles are in different
languages.  This avoids ping-ponging between LTR and RTL styles for
chapter numbers, etc.

Also reset language when entering figure environments, and use
\itshape and \emph instead of \it and \textit (respectively).

Change-Id: I8dcc7ad8571a47a23b9e0e1e9c7d66dd07f039c4
Handle missing keys more gracefully in Db module.

Change-Id: Id38aae19d81b842d3f931011b5baa10299430a39