Banner template validation

[gbirke]

Add validation code that connects the sensitive banner to the server for validation and data submission.

[wmde-manicki]

Generally looks really good. Data is validated, if all is good then user is transferred to the donation website. Donation data is stored in the database. (Tested on my local instances but there is also test running on test.wikimedia.de, so I assume we can say that it works).
Below some remarks that I've noticed:

• this depends on banner-template-validation for obvious reasons. I'd like to merge static banner upgrade form #3 quite soon (actually even right now). Could you make this a pull request onto master once that PR is merged? It'd also make reviewing easier when there is a single actual PR instead of two monstrous PRs combined into one
• on the SEPA agreement page (second step of the Lastrschrift donation) links to change address data, payment data and the amount do not work - this might not be issue in the scope of this particular PR but should definitely not be forgotten
• Error boxes are there when I hide the form and open it again - this is actually good. I am just wondering whether error box regarding amount should actually hide when hiding the form?
• another thing regarding the the error box about the invalid amount - it covers the Lastschrift button. I don't see any better place to put the error message so it wouldn't hide anything else. Maybe there should be some way to hide the particular (or all) errors? How about discussing this with Henning?
• also the thing to consider, possibly not requiring a change: maybe the message about inserting valid amount when e.g. entering 0.50 when donating with credit card is not that informational? Maybe it should explicitly say what amount could be entered?
• Looking for it briefly in the code I have not noticed that it is requiring user to tick the fields in SEPA withdrawal agreement page (SEPA-Mandat)
• is donating with direct debit (Lastschrift) actually possible right now? I did not notice BIC (and other bank data) being "generated" from the IBAN (this might not be in the scope of this PR), but also nothing seem to happen when I fill data in all fields of direct debit donation and click the yellow button on both steps. It just folds in the form. Same actually happens when I enter no data and just click "proceed". It might be something with my dev instance as some strange things started to happen while I was testing this. So if you say that this payment method should work as good as others, I'll try it again.
• I'd really not want to merge any pull request that is failing on CI. Especially when those JSHint complaints seem sane. Could you please fix those? At least by adding a commit fixing the issue.

[gbirke]

Thanks for all the comments.
I've talked to Henning about the obscured buttons and we decided to leave them obscured for the time being.
I've tried to give valid amounts in the error message but this will make the tooltip to long, breaking it over two lines and generally boing very ugly. Don't know how to solve that.
I've created a new commit that fixes the JSHint violations.

I will close this PR now and create a new one against master as soon as I have addressed the other points (SEPA mandate validation and BIC generation)