Improve gw fee

Denominated more items in Bits. 

Please pay special attention to my modifications at line 16 of the gatewayModel.js file, to which I have added a small comment, and line 33 of feeView.js. 

TO DO: 
Line 33 of feeView.js is an attempt to handle the use of Bits instead of mBTC on the frontend only, and should be replaced by the appropriate change in numbers on the server.