Best effort validation of user input

[zstyblik]

PR adds best effort validation of user input. Fall back to sane defaults in case of invalid input.

Fixes #22

[zstyblik]

First of all and as before, I'm no Java programmer. Second, I haven't found a better way to validate user input than to do it this way, resp. via checkUrl call or whatever it is. There is a drawback, though. Yes, message pops up and warns the user, but it doesn't prevent user from submitting invalid input. That's where third thing comes in - defaults. I think it's better than to throw an exception. Though, I perceived the code to be ugly.

@jovandeginste, please, can you give this a look?

[zstyblik]

I have refactored the code a bit and added unit tests. Unfortunately, I have no idea how to write unit tests for form validation part.

[zstyblik]

... or @jippi ?

[jovandeginste]

@zstyblik Due to personal stuff, I'm taking some slow weeks.

As a default, I would rather have the code throw errors than do something I didn't expect it to do.

[zstyblik]

@jovandeginste sure, no problem.

As a default, I would rather have the code throw errors than do something I didn't expect it to do.

I'm open to suggestions. However, Java exception says pretty much nothing to the user like any exception from any programming language and code you're not familiar with. In other words, I really hate when Jenkins goes exception on me for no obvious reason.
Anyway, give this patch a try and you will see. Also, as I've stated above, I haven't found way how to prevent form being submitted.

EDIT: Let me rephrase it a bit. I'm talking about communicating the error to the user. Defaults are used as the last line of defense when form validation errors are ignored and form is submitted regardless. If it's possible to raise exception which is easy to understand by the user, let's do that.

[phedoreanu]

@zstyblik Would you please rebase and add the security fixes from #42 ?