repomaker/issuebot API fixes

Repomaker and Issuebot both use fdroidserver as an API. I also just wrote a script that builds repos from other repos like what repomaker does, and it also uses fdroidserver as an API. These are specific fixes from that effort. One particular change, accessing app as a dict rather than an metadata.App instance, should be used throughout fdroidserver functions that can be used as an API. The metadata.App class is just syntactic sugar to avoid typing brackets, e.g. app.packageName rather than app['packageName']. So syntactic sugar should not get in the way of functionality.