Change endDate on the fly

[martinkrung]

[martinkrung]

A flexible end date could be used for:

1. Make the token sale longer

• some sales get traction only to the end. (They have been too short, and the community activation takes longer than expected.
• outside events like scams, market turmoil, infrastructur problems or high gas days slows down the sale

Only makes sens, if the demand is growing and some token left.

2. Make the sales shorter

• Are sold out, to finish the sale - better fix this over a forced closing?