[FIX] Notifications should include executed trades (RT-1667)
[FEATURE] Add Trend in Balance

Also crafted the auto-width dropdown.
[FEATURE] In Send/Convert, user should be able to specify the gateway (RT-1790)
[FEATURE] Export history as a .csv

Add rpDownloadCsv attribute to rpDownload directive to specify that data
is downloaded as csv format.
[FEATURE] Export history as a .csv

Add button that triggers download of displayed History to CSV file.
[FEATURE] Export history as a .csv

Add exportCsv function and associated helper functions to extract the
displayed Transaction History into a string with a comma-delimited line
for each history entry.
[FEATURE] Export history as a .csv

Add getAmountSent function to calculate the amount sent if possible.
This was refactored from loadTx() in tx.js

In processTxn, add the following to returned transaction object:
- amountSent:  (together with currency if not XRP)
- sendMax: SendMax if it exists as an object (not if just String)
[FEATURE] Export history as a .csv

Move code within loadTx() that calculates amount sent to getAmountSent()
in jsonrewriter.js and invoke that instead.

NB the code that was moved to getAmountSent() has been changed to fix a
bug: the amount sent was not being calculated when the send and receive
currencies are different and one of them is XRP.
[FEATURE] Export history as a .csv

Correct for renamed function getAmountSent
[FIX] Space on unfunded accounts banner