Repetitions editor: Activate/deactivate target repetitions

• users are not used to batch edit target repetitions
• and target repetitions are not very well distinguishable from source repetitions in the rep. editor

add a category to the rep. editor under "Decide individually for each rep." see screen:

[  ] exclude by default target repetitions, that are not also source repetitions
[  ] Zielwiederholungen standardmäßig ausschließen, die nicht auch Quellwiederholungen sind

=> If this option is checked, then in the repetion editor pop-up still the target repetitions that are not also source repetitions are listed, but not checked for being replaced by default

add a config for system/client

Autopropagate / Repetition editor default behaviour for "individual" and target repetitions

Defines default behaviour for repetitions editor: if enabled, exclude by default target repetitions, that are not also source repetitions

Default for the system setting should be "enabled"