paster: add informational/dummy "upgrade-db" command

The command is placed kallithea.lib.dbmigrate:UpgradeDb (which was the
location of the old command, too), to ensure that "paster upgrade-db"
continues to work, even if Kallithea is installed in "editable" mode
(setup.py develop/pip install -e) and package metadata has not been
updated (and also to prevent issues caused by stale .pyc files).

kallithea/lib/dbmigrate/__init__.py

@@ -0,0 +1,8 b''
+from paste.script.command import Command
+
+class UpgradeDb(Command):
+    hidden = True
+    summary = '(removed)'
+
+    def run(self, args):
+        raise SystemExit('The "paster upgrade-db" command has been removed.')

setup.py

@@ -180,6 +180,7 b' setup('
     cache-keys=kallithea.lib.paster_commands.cache_keys:Command
     ishell=kallithea.lib.paster_commands.ishell:Command
     make-index=kallithea.lib.paster_commands.make_index:Command
+    upgrade-db=kallithea.lib.dbmigrate:UpgradeDb
     celeryd=kallithea.lib.celerypylons.commands:CeleryDaemonCommand
     install-iis=kallithea.lib.paster_commands.install_iis:Command
     """,