Previously the federation layer has written the empty string to the
database, now it writes nil/no value to it while our code still expects
the empty string in some cases. Restore the old assumption by returning
the empty string, the real raw value by now is available again in
StatusMessage#text for those that need it, such as validations or tests.

Improve ConnectionTester

start cucumber jobs before other jobs

the whole build is faster, if the workers start first with the longer
running jobs.

bump diaspora_federation to 0.1.1

This fetches reshare roots if they are not available locally already.

ignoring the error message

Previously it returned the return value of Logging::Logger#warn, which
is true for loggers that log the warn level. However
Diaspora::Federation::Receive::receive_relayable checks the return value
for truthiness in order to decide whether to attempt to relay it,
resulting in a NoMethodError: undefined method `parent' for
true:TrueClass in Diaspora::Federation::Receive::relay_relayable

This change is cosmetic as the exception raised prevented any action
that shouldn't happen anyway, so there's no actual logic change.

fix sender for messages for old pods

Send a second message to remote recipients with conversation-author
as salmon author if the conversation-author is local.

The first dispatch will fail on old pods. New pods will ignore the
second message, if the guid already exist.

Fix relayable retraction sender

use the parent author as salmon sender, if the parent author is local

Federation rewrite with diaspora_federation gem

the check that the participation parent author is local is now done in
the diaspora_federation gem

send retraction for relayable to target author if retracted by parent author

* remove author_signature column
* delete all self-participating participations
* delete all participations where author and post-author are remote
* delete all duplicate participations
* delete all participations without post
* create unique index

only deliver to parent author