Implements OKAPI access for opencaching.de

So, in my opinion this is now ready to go to master, be reviewed and tested.

The three commits in this PR implement:
* A checkbox in the settings to switch of geocaching.com access for livemap and searches
* A utility to create an AttributeParser fro OKAPI attribute strings (only localized strings available there, no ids yet)
* OKAPI for opencaching.de

For the latter there are several things noteworthy:
* The OAuth-Keys are now in a separate string resource. After merging you need to copy the file from template to res/values to compile. For OAuth to run you need to obtain a ConsumerKey and -Secret via http://www.opencaching.de/okapi/signup.html and put it in there. mucek4 should get an 'official' one for Jenkins.
* I generalized the OAuth-related classes to support twitter and opencaching
* I created a derived OCapiLiveConnector that allows nearby and viewport searches and support logging.
* To separate logging from GCParser I created ILoggingManager which allows for the preload activity necessary for gc, but also supports the straight semantics for OKAPI. See this as a first version with room for improvements.

Comments and criticism welcome as always