Build script changes.

- Replace more placeholders in config.xml/package.json/manifest.json.
- Bugfix: Opera OEX doesn't include source directory anymore (making it invalid).
- Opera: Installing and updating from server works.
- Firefox: Installing and updating from server works. Which took a lot of work. Very annoying. VERY annoying. Very ANNOYING. Guuh, I know, security and all that. But from a developer point of view that was a terrible experience. Needing an extra tool (commandline patched mccoy) to sign the update.rdf and to include an update key in the install.rdf which was ALREADY PACKED in the XPI. And OF COURSE the SDK tool CFX doesn't just have a parameter for adding the updateKey while it generates the XPI. No, that would be too easy now, wouldn't it? /rant