check for empty bottle based on time interval

(add BOTTLE_EMPTY_INTERVAL in delay_until)
remove accidently commited file
add .org and .rej to gitignore
fix delay_until for use without pouring
fix return code checking of delay_until for cup waiting
comment out debug serial output in delay_until
handle scale error when measuring cup weight
fix -inf values as init values

we cannot use the min int value --> int overflow if cur is subtracted!
(also updates some comments)

Note: this is the first commit done alone, before session together with
Jakob.
move waiting for cup to function in lib/ads1231
fix waiting for cup

WEIGHT_EPSILON already in delay_until
WIP this is a draft for pause/resume