Upgrade to oemof.solph 0.5.2

[FelixMau]

Upgrading to oemof.solph 0.5.2 should enable use of tsam integration in tabular.
Will also fix #150 and #155
Moreover always a good idea to keep dependencies up to date :)

[FelixMau]

In favor of faster development and to move on with current project. The upgrade will only be towards oemof.solph 0.5.2dev2 to be matching oemof.solph feature branch of tsam integration for now. Nevertheless we will keep this issue open, as an update to 0.5.2 is necessary for further development.