Show sum of selected transactions in 'Transactions'-tab

[crowning-]

References:
http://jira.darkcoin.qa/browse/DRK-138 (JIRA)
https://dashtalk.org/threads/enhanced-darkcoin-wallet-ui.1705/page-22#post-53222 (dashtalk)

Much more convenient than selecting those transactions, export them and compute the sum with an external program.

Looks like this:

Builds fine with Gitian and runs on all 3 OS without problems.

[UdjinM6]

Looks good! 👍
However it works only for shift + mouse click for me (on Mac) and doesn't work for shift + arrow keys and mouse down + mouse move + mouse up Though it's not a big issue but maybe you can fix it too? :)

[crowning-]

Good point, right now I only send signals to the transaction-list when there's a click event.

I'll have a look later today and report back when it's ready to merge.

[crowning-]

Adding shift + arrow keys and mouse down + mouse move + mouse up: probably one of the most expensive fixes so far, 8 hours for one line of code.
(actually 1 minute for adding the code, and 479 minutes for figuring out why it doesn't work at the place where I put it and trying one million things to work around the problem )

@evan82 , it's ready to merge.

[UdjinM6]

Everything works fine for me now! Good job! 👍