Add sortBy and order fields to xapian bridge API

Allows client to sort result set by a given xapian
value.

Rory & Roberto

[endlessm/eos-sdk#2133]
Merge pull request #33 from endlessm/sdk/2133

Add sortBy and order fields to xapian bridge API
Rewrite xapian-bridge in C

This commit ports xapian-bridge from GJS to C. The port is meant as a
drop-in replacement for the former code, with 1:1 compatibility.
Convert tests to gtest

Convert our unit tests to C tests using GLib's gtest.
Remove eos-jasmine submodule

Now that our tests are in C, we don't need this anymore.
Move systemd files to main branch

No need for these to live in the debian branch. They're useful on
non-debian systems as well.
Update .gitignore
Merge pull request #34 from endlessm/wip/c-port

xapian-bridge C port
build: don't require gobject-introspection

We're not using it anymore.
main: print a critical warning when database creation fails

Like we do in the GET method.
xb-main: reorder checks

This will be useful in the next commit.
xb-main: unescape the path we get in the query

Paths will typically be passed-in escaped in the query. Make sure we
unescape them.
tests: escape paths before passing them to the bridge

Should fix test failures seen on OBS.