Allow configuration of combinations and/or long-presses

[tcdude]

From what I can tell, the configuration currently only allows to assign single, short presses of buttons. Special events such as long-presses and/or pressing multiple buttons at the same time are hard coded and are not directly user configurable.

I would propose enhancing the config file and parsing as follows:

• Instead of looking for hard coded keys (i.e. button1, button2, ...), maybe loop through the available keys and evaluate the key
• To enable combinations, keys could be a series of buttons concatenated with the symbol +
• A prefix could be defined to indicate that the button or button combination that follows only applies for long pressing that combination