[balooctl] Reduce nesting level for addOption arguments, cleanup

Summary:
The high nesting level makes the call hard to read, split it up.

Cleanup i18n somewhat, add context, remove "default" from the verbatim
option value, i.e. make it translatable. Remove trailing/spurious
whitespace.

Test Plan: no functional change

Reviewers: Baloo, Frameworks, ngraham, poboiko, astippich

Reviewed By: Baloo, ngraham

Subscribers: kde-frameworks-devel

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D20041