Take focused window to new context, Remember renamed workspaces

[jooooscha]

Hey, I would like to revive this project and have started with two features.

First, I have implemented a minimal solution for #2. This can probably be extended to be more useful. Currently, it only supports taking a window with you when switching contexts. It does not support just sending a window to another context.
Also, I noticed a bug, which probably only occuers in combination with Smart Borders.
When taking a full screen window (so no borders) from context A to context B and the window is not full screen in context B, the borders are missing. A workaround is to switch to another context and then back.
I have tried refresh and rescreen but they don't solve this. I am not too deep into XMonad to tell how to solve this

Secondly, I am using NamedWindows, so I have implemented that the named workspaces are stored per context.
This should not influence the behavior when not using NamedWIndows, but this is untested.

I am happy to explain any part of the code, or change or remove parts from this PR.

PS: While trying to understand how this plugin works, I have renamed some variables. I think they are a bit easier to understand now, but if you want, I can change them back.

[Procrat]

Thanks for your interest in this plugin, @jooooscha! Great to see a PR! I'll have a closer look at your code when I find the time, but I'm afraid I can't make any promises time-wise.

[jooooscha]

Did not realize that changes would be automatically reflected in this PR. Those three new commits are not directly related to the original feature (I think they are pretty cool, still :D).

Just for the protocol, they extend the original feature by fixed workspaces. The workspace switching functions can now be called with an array of workspace tags (not the names; when using named workspaces). Those workspace tags are now fixed and will not be switched to the new context. I am using this, for example, for my music player, to which I want direct access in all contexts.

Internally, the fixed workspaces will be copied to the new workspace at every switch. Therefore, one window can be on two contexts, and when deleting a context the window would also be killed on the current context. Therefore, I have also adapted the deleting function, to only kill windows not on a fixed workspace