fixed and greatly simplified delay implementation

While it was always allowed to use arbitrary expressions for the
argument to delay(), this never worked as one would expect if the
expression depended on e.g. monitored variables. The reason is that
previously the delay expression was evaluated once for all delays
appearing in conditions inside a state when the state was entered.
Later checks whether the delay has expired used the cached delay
value.
Now, delay expressions are evaluated like all other parts of the
state transition condition and seq_delay() takes a double argument
instead of a delay id. As a (transparent) side effect, if the
delay has not yet expired, the minimum time to wait for events is
adjusted. This adjustment is now more precise, since we do not store
the delay but rather the (future) time when the wakeup should happen.
The new implementation makes a lot of code obsolete which has
consequently been deleted:
- type DELAY_ID and all mentions of delay ids
- assignment of delay ids in the compiler
- the special cases FT_DELAY for the delay() builtin and
  the special E_DELAY syntax node type
- generated delay init functions
- seq_delayInit()
- clearDelays() and calcTimeout() in seq_task
- array members delay, delayExpired of struct state_set
  instead there is now double wakeupTime
- member numDelays in various structs
- assign_next_delay_id in the compiler