possible to reuse the header view when sticky and when not

[farfromrefug]

First thanks for your great library. I love it!
Now i did not really like the fact that when a header switch from sticky to normal (and reverse) you actually expect a "new" view to be created.
I prefer to actually reuse the the section header. That commit allows that.
Mostly the only changes are:

• make sure the headerView has no parent to prevent exception on addView
• when removing "sticky" header, add it back to the WrapperView if necessary

How you'll like it ;)

[emilsjolander]

Sounds good. Some first thoughts!

• Some duplicated code blocks
• Need more comments to explain things, lot's of stuff i don't really understand what you are trying to do
• Indentation needs to be fixed

[farfromrefug]

Ok :

• what indentation settings do you use?
• can you point out the duplicate code blocks?
• I'll try to add comments in the days to come. But you know it takes time. If you can point the places you don't understand, i'll comment them specifically

Thanks

[farfromrefug]

I just added a bunch of changes.
It allows better use with ListViewAnimations.
If at the end you prefer it separated (but i dont really think it s necessary as it it still mostly refactoring) i could create another PR