Garbage collector-like feature

[mrfatguy]

Please, implement and additional slider or dropdown that will allow to configure how many times (n) app retries to send all the measurements that hasn't been confirmed by the server side as received and saved in the database.

Logic assumptions:

1. An additional (next to Different data read and data send intervals #18) loop that iterates through the send queue and resends unconfirmed measurements.
2. When n > 0 and given measurement is still unconfirmed after n retries then it is removed from send queue.
3. Unconfirmed measurement is sent with their own / original timestamp, not the current timestamp.

Setting this slider or dropdown to 0 means: repeat endlessly. This should be the default value.