Make hive.get_info return more relevant version information

While Hivemind has undergone constant updates lately, hive.get_info does not return values that are directly exploitable or relevant. ex:

{
   "hivemind_version": "0.0.1",
   "hivemind_git_rev": "0ca3cd16",
   "database_schema_version": 18,
   "database_head_block": 50150419
}

version does not mean anything. Was there a version 0.0.0? database_schema_version is not more interesting because the DB structure has been revamped several times and this value has not been updated for ages.

The only value that reflects up-to-date version information is hivemind_git_rev but it is cumbersome to have to parse the git history and check the commit tags to compare with other nodes and know which one is running a recent version of the code.

I suggest adding at least a hivemind_git_date value which provides us with something easier to compare (it can be retrieved with git show -s --format=%ci <commit>).

Having hivemind_version and database_schema_version updates would be the icing on the cake.