Fix editing amount of a transaction

[humdingerb]

Only validate split items if the SplitView is actually shown, which makes the transaction a "split-transaction". Only then the original amount cannot be different that the split-total.

Fixes #100

[humdingerb]

@dospuntos , hope I didn't step on your toes and the fix is good.

[dospuntos]

@humdingerb no worries. Looks good, maybe disable (and reset) the amount box when fSplitContainer is visible?

[humdingerb]

Good call!
I amended the PR. Also resized the window when hiding the SplitView. That's been bothering me for a while... :)

Could you finish the Latin American Spanish, so we can export it all and release tomorrow?
Or do you have any other things that should be committed before release?

[dospuntos]

I completed the Latin American translation. I don't have anything else that should be included, I think your PRs have included the most pressing items.

[humdingerb]

OK, I mailed the translator for Catalan if he could finished that one, too. He didn't get backto me yet. Let's give it another day and release tomorrow, with or without a finished Catalan.

What do you say about #113 (comment) , go with the PR as is, or force capitalize category names?

[humdingerb]

Assuming you're OK with how #113 does it for now. We can change later if needed.
Let's get that release out. :)