More input contetxt usage

See commit messages. It uses the input context where the function `input(long ch)` has been used before. The changes make that function obsolete and it has been removed.

I moved the code of `get_keypress` into `get_input_event`. Calling `get_keypress` from a SDL build would create a infinite loop as `get_keypress` calls `getch`, which in SDL is a wrapper around `get_input_event`, which calls `get_keypress` and so on.