Remove check for plugin library

[sbusch42]

Rewrite plugin system, so that

• [x] Plugins register their components on load
• [ ] Plugins do not need to expose any functions anymore
• [ ] Checks for the existence of such functions and automatic unloading are removed

[cgcostume]

is this still relevant?

[scheibel]

I remember working on the last two items...i'll have to check if it is implemented.