normalize CurrentVersionCode/suggestedVersionCode/upstreamVersionCode across the project

• fdroidclient has App.suggestedVersionCode and App.upstreamVersionCode
• fdroidserver has CurrentVersionCode:
• index-v1.jar has suggestedVersionCode:

This stuff should be normalized across the project, both in terms of the names, and what they represent. I think that the name suggestedVersionCode: should be used as the same value across the project: the versionCode that F-Droid will auto-update to. In other words, it is the version of the app that F-Droid suggests users install.

In fdroidclient, that's called App.upstreamVersionCode, while App.suggestedVersionCode is the combination of suggestedVersionCode:, the compatibility of the APKs, and the availability of the APKs.

for related discusssion, see #1052 (closed)