h-rider creates too many threads

[icher-g]

each time the table is populated h-rider starts new thread to count total number of rows. if a table is too big this operations might take a long time and while user populates other tables those threads remain alive and running creating additional pressure on the hbase.

[icher-g]

The timeout for counting a total number of rows has been introduced. In addition if another table is selected the current calculation is canceled.