Check for DeepSea version requirements

openATTIC currently simply assumes that it's communicating with an up to date version of DeepSea when it submits API requests. As DS is installed on the Salt master node, it's not easily possible to ensure that a certain version of DeepSea is installed as required by openATTIC (e.g. using RPM dependencies during installation).

Currently, if the DS version on the master node is too old it would likely simply fail with obscure errors.

This should be handled more gracefully - e.g. by checking the DS version number and creating a proper error message if version check failed (e.g. if it does not meet a defined minimum version).

In order to accomplish this, DeepSea first actually needs to provide this information - I have submitted the following issue on github about this: Provide an option to return the DeepSea version via cli / REST API