Would there be any application or method of controlling the charge level and limiting it for example to start charging at 20% and stop charging at 80% ?
You could use Tasker to make a beep or push a notification when battery level is ouside your safety boundaries, so you can take an action by yourself (ie. un/plug the charger).
The following image shows an example of configuring Tasker to take an action depending on battery state:
Application: No, as for an application to do this, the answer is no since charging on an Android phone is done by its hardware! The software has nothing to do with the actual charging of the phone! (This is why your phone is able to charge even when the OS is powered down)
Method: No, since the charging is not controlled by the software of your phone, this means it will be very difficult to stop your phone from charging (since there is no software modification that I can think of that will help... I could be wrong!)
However, as pointed out by Francisco Alvarado earlier you could create Tasker profiles to notify you about custom charge levels. Or if you are very paranoid about maintaining battery health you could make Tasker prompt you before automatically shutting down (just a suggestion).
Well one way of doing it would be with a device such as Raspberry Pi or similar (perhaps with java installed on it). With an add on such as Laika it can control devices including relays which could turn on/off the power to a charger. Since Android to PC communication is available over USB https://stackoverflow.com/questions/3803871/android-apps-communicating-with-a-device-plugged-in-the-usb-port then I'm guessing an app could talk to the fruity device, if not it could post to your own hosted web service. The app could then tell the device when to turn on the charger and when to turn it off according the the apps settings.
OK, a bit over the top and would need experimentation, but I think it could be done.
Lets hope that Android Marshmallow (or Maltesers or M&Ms or whatever it is) will have this built in for hardware that can support it.