[WIP] Introduce SplitButton

[QuantumDeveloper]

Introduced new control - SplitButton

[QuantumDeveloper]

Here is the result. @Amrykid @punker76 What do you think?

[QuantumDeveloper]

Second try:

Basic:

Focused:

MouseOver:

[zeluisping]

Chevron is too big. Maybe reduce size to something like 70-80%.

[amkuchta]

I was actually thinking a small triangle might be more in line with the style of everything else in MahApps

[Sorien]

arrow is too big for sure, maybe i'd use something like this

[zeluisping]

arrow

It's actually called chevron.

[QuantumDeveloper]

I hope this is what you wanted?

[zeluisping]

Move it a bit to the right.

_Edit:_ I mean Left.

[QuantumDeveloper]

Third try:

[QuantumDeveloper]

@Amrykid you could merge this PR.

[chandramouleswaran]

This is good work - did you take a look at https://wpftoolkit.codeplex.com/wikipage?title=SplitButton

Wouldn't adding theme to the above make more sense than reinventing the wheel?

[zeluisping]

@chandramouleswaran Adding a theme to a control from another library would create a dependency on said library. Creating the control makes MahApps.Metro more independent.

[QuantumDeveloper]

@chandramouleswaran also their split button is not good enough for me. Thats the reason I made my splitbutton. And the quality and speed with which xceed fix bugs and update controla also non-suitable for me.