Async Validation and prevent activity auto closing when completed

[thedumbtechguy]

Changed validation to use a callback therefore allowing for async validation
Removed finishing of activity when form is completed

fixes #12 and #11

[heinrichreimer]

Overall veeery nice pull request!!!
Just two suggestions:

1. Move StepCheckerCallback in Step.java
2. Give users the ability to use public void check(..., StepCheckerCallback callback) {} or public boolean check(...) {}. I'm not yet sure how to implement this but it should work with an abstract class. Any thoughts on this?
   Thank you!

[thedumbtechguy]

No idea why, I almost missed the notifications. I will check and see what I can implement in the mean time.

[thedumbtechguy]

As per your suggestions,

1. Done
2. I am thinking rather than changing the API totally like I have and having to bump the version number totally, I can make each Step have an additional constructor which accepts the original StepChecker. Then rename my implementation to StepCheckerAsync.
   The new constructor will wrap the StepChecker in a StepCheckerAsync making the internals consistent.
   That way, we allow the user the flexibility and maintain the original Major Version of 2 and bump it to 2.1.0.

[thedumbtechguy]

Done. Kindly review.

Also, I think we need to move to the builder pattern. The constructors have become more cumbersome. If you do merge this pull, I will work on it.

[heinrichreimer]

Ok, really awsome changes. It presumably sounds like I'm a smart aleck, but I heve still some little points to mention:

1. Move StepCheckerCallback into Step.java
2. ProgressDialogs are a bit old-school and also userunfriendly and hard to style. Let's change that for a simple layout: It should be a FrameLayout and a centered, vertical orientated LinearLayout in it. In the LinearLayout there should be a horizontally centered ProgressBar and a horizontally centered TextView with a customizable "Loading..." text. Both the ProgressBar and the TextView should be colored based on the theme colors.
   Thumbs up for your work!

[heinrichreimer]

BTW, great way to achive consistency AND new features using StepChecker and StepCheckerAsync 👍

[heinrichreimer]

@frostymarvelous Builder pattern belongs to #8

[thedumbtechguy]

Oh, I didn't notice the StepCheckerCallback was out again. I did the work in a separate branch ahead of master and realised this, so I basically just copied all the files into the master branch. Fixed.

Are you sure you want us to implement the progress? I only used the progress dialog as part of the demo.

[thedumbtechguy]

Why I ask is because I feel the library should focus on doing what it does best. We will be incurring technical debt by adding unrelated features.

[heinrichreimer]

The ProgressBar should only be used if the validation is async. Either way progress indication and a 'completed'-screen are very common uses and therefore belong in this library IMHO. Would also be nice if we swap the ProgessBar with an ImageView showing a big check mark to indicate the end of the form. I await my summer holidays, I'll be able to work on the library then.