Accept share input size in bytes, KB, MB and GB

add dropdown to accept the different size scales
implement the logic which converts user entered share size into bytes
Merge branch 'issue#19_share_input_size' of git://github.com/Mchakravartula/rockstor-core into Mchakravartula-issue#19_share_input_size
Remove Bytes from share input size dropdown.
Add TB in dropdown and change size scales to KB,MB,GB,TB.
Merge branch 'issue#19_share_input_size' of git://github.com/Mchakravartula/rockstor-core into Mchakravartula-issue#19_share_input_size
Merge branch 'Mchakravartula-issue#19_share_input_size'