It takes for granted that the certificate is valid from the very same
date it's downloaded.

I've also fixed another message: if a file to be downloaded is not
found, we say the entered provider isn't a LEAP provider. This is based
on the fact that if provider.json doesn't exist/contain valid
information, then the url isn't pointing to a LEAP provider.

We don't assume ca.crt is in /ca.crt anymore, but fetch the complete url
from provider.json.

We also signup against users.json file instead of simple "users", which
worked for *.bitmask.net domains.

Functionality copied to the Release build.

This has the problem of localized messages. irc log questioning:

May 8th 2014
08:12 <@parmegv> mm, I was thinking... I was rephrasing the error messages given by our api during authentication
08:13 <@parmegv> I thought why should I rephrase it and think twice
08:13 <@parmegv> so now I'm just "pretty printing" the error message given by the api
08:13 <@parmegv> but that has a problem: they aren't localized
08:14 <@parmegv> would implementing a localized version of our error messages be useful?

A bit of refactoring too, sendM1 much simpler.

There is some problem in the maths, because the server says it's ok but
login doesn't work from Android app nor from webapp.