[mlite] Do not install translators from desktop files

In Qt, every translation goes through list of globally installed
translators linearly. Non-discriminately loading translation
catalogs specified in .desktop files risks name clashes and slows
down translation.

This commit loads translation files first time they are needed,
and the results are cached.

Also, engineering english support is removed.
Merge pull request #19 from mikkoharju/translators

[mlite] Do not install translators from desktop files