WIP: Mirror support

Addresses #35

mentioned in issue #35

marked as a Work In Progress

changed milestone to %1.0

added bazaar label

Now has mirror support for the index.

https://gitlab.com/cde/fdroidclient/commit/d3651f8c5b0aad251054bc27fc46f713ad1435fe contains the bulk of the changes, and I've tried not to re-invent things by simply re-using both the previous index download code, as well as the getMirror() function from InstallManagerService

TODOS / Notes:

• Make more functions as needed
• Find a good, generic place for getMirror() currently present in both InstallManagerService and IndexV1Updater, alongwith supporting variables
• Unsure about the while loop I added in IndexV1Updater to deal with the mirror. Any better alternate suggestions? My basic instinct was to not touch the current download code at all, so it doesn't affect any existing installs where the downloads already work.

resolved all discussions

resolved all discussions

I moved the getMirror() code to FDroidApp.java, that function is what keeps track of the lastWorkingMirror, and also retry / timeout logic. However, while the code is shared, both the index download part and the app download part reset those variables before download for now, to avoid added complexity, and to avoid changing the current download code.

I.e., all of this new mirror code is used only after we get ConnectException | SocketTimeoutException while downloading from the default address. This holds true for both index and app download.

changed milestone to %1.1