mobile: No cloud repo creation more explicit

Before this change, there was only one way to create the local
no cloud repo on the device. The user needed to add at least
one dive to the no cloud account (so that there is something
to save). While this worked in some scenarios, it could also
get things in an inconsistent state: credential status = CS_NOCLOUD
but no local repo. This was a dead end.

In this commit, the creation of the no cloud repo is made more
explicit. When asking for no cloud mode, just create an (empty)
repo for it when it does not yet exist, and otherwise, just
open the existing (possibly empty) repo.

Now, a user can have no cloud repo, next to (any number of)
cloud accounts.

This leaves one functional aspect left: how does a user abandon
the no cloud repo, by merging his data into a true cloud
account. This is code for this, that tries to do this merge in
a smart way. This seems to be broken (too). To be clear: this
is no part of this commit.

Fixes: #667

Signed-off-by: Jan Mulder <jlmulder@xs4all.nl>

mobile-widgets/qml/CloudCredentials.qml

@@ -148,6 +148,7 @@ Item {
 					manager.syncToCloud = false
 					manager.credentialStatus = QMLManager.CS_NOCLOUD
 					manager.saveCloudCredentials()
+					manager.openNoCloudRepo()
 				}
 			}
 		}