Rename dcline to simple_dc_link

[jkisse]

Feature Checklist

• Searched the issues page for similar reports
• Read the relevant sections of the documentation
• Browse the tutorials and tests for usefull code snippets and examples of use

Issue

The two components dcline and line_dc can easily be confused and the documentation is not very precise in pointing out the difference between the two. I propose to rename "dcline" to "simple (HV)DC-link", as the electrical model apparently assumes converter stations as well.
The documentation and docstrings should be expanded and also mentioned, that dcline and line_dc are two completly different things and not intended to be used together.

Label

• Relevant labels are selected

[vogt31337]

Really quite confusing, but I don't understand what a line_dc is? Where is it used and for which use case?
The dcline is modeled using generators but from the docs a line_dc seems to be a normal line? Is this for dc loadflows?!