[addresses issue #713] Added eCryptfs under 'File encryption' section.

Also added: translation stubs in all json files in lang/ & a 50x50
256-color non-transparent png, ecryptfs.png, at lib/img/free/

This commit is based on 3d0222c10c79c0a, which was HEAD commit in the nylira:master. If the HEAD is moved to a different commit by the time this pull request is reviewed, please ask, I'll rebase it on top of the latest HEAD.