Revert/adapt "fix/simplify Community._download_master_member..." to a
static interval LoopingCall.

This reverts commit 0aaad467a7ef2f7cf2e4de0bef040462a9819ac2.
_pending_tasks is a dict now, implemented cancel_pending_task(),
_batch_cache doesn't store the Cache DelayedCall anymore as it was
stored in _pending_tasks too.
Typo and cleanup
Use a dict for the request timeout delayed calls
Fix the call on reactor thread decorator
Move the retrial loop to receive_messages so all the tests can benefit
from it.
Fix and move the reactor call decorator to util.py and refactor all the
unit tests to use it.
Convert test_nat_detection.py to unix newlines
Cleanup
Set the master member download interval to 15 secs
Move all the decorators and the memory dumper to the util.py module.
Use the Community fast walker functionality
Remove all remains of bootstrap timeout functionality.
Port the inactive community cleanup loop to twisted
Merge pull request #243 from whirm/twisted-callback

Twisted callback
move add identity logic out of Member.has_identity()
move SQL out of DummyMember constructor
create init_community() for community init logic
remove loading identity message in dispersy _store()
small changes