Support translating UTF8 strings

Interpreting UTF8 encoded strings using tr() instead of trUtf8()
and encoding the string back to utf8 again leads to serious encoding
errors.

Fixes #230

Signed-off-by: Maximilian Güntner <maximilian.guentner@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Escape all problematic characters when saving a tag

Signed-off-by: Maximilian Güntner <maximilian.guentner@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
changed tag completition to case-insensitive

When completing tags, the case of the completion prefix
should not matter.

Signed-off-by: Maximilian Güntner <maximilian.guentner@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>