Remove compiled message catalogs

A kind of binary files are useless to be maintained in git repo.
I18N team and package distributors have agreed to remove compiled
message catalogs from Horizon git repository.

The instruction on how to compile message catalogs will be
covered by https://review.openstack.org/#/c/126169/
or the installation guide.

DocImpact

Change-Id: I81b05cf79c21d85bed8a6da6df659955e7ac58c5
Closes-Bug: #1196982

.gitignore

@@ -1,3 +1,4 @@
+*.mo
 *.pyc
 *.sw?
 *.sqlite3