Bump platform and minimum client versions for soledad

#6160 (closed) was produced by shipping a bundle with the develop branch of soledad before it had been tagged and properly tested. Seemingly, the 0.6.x branch of the client is not compatible with 0.5.x branch in the server, but this fact has not been properly reflected in the client and soledad version pinning, neither in the platform (which should specify a compatibility string so that the client properly complains about the versioning problem).

After pinpointing what's exactly the incompatibility problem, we should probably need to:

(1) bump whatever version string the platform offers to the client (2) bump the minimum soledad versions needed in bitmask client

Note that this affects "Bitmask Desktop 0.7.0" but that target is closed now.

(from redmine: created on 2014-10-07, closed on 2015-03-03, precedes #6160 (closed))