Added new props called backgroundColor which sets the backgroundColor of the signature

[john1jan]

• Added three new props for setting strokeColor, minStrokeWidth and maxStrokeWidth
• Added new props called backgroundColor which takes any color string which supports #RRGGBB #AARRGGBB 'red', 'blue', 'green', 'black', 'white', 'gray', 'cyan', 'magenta', 'yellow', 'lightgray', 'darkgray'
• Add feature for setting background as transparent. just set backgroundColor="transparent".
• Removed showBorder as its not required the developer can set border for the container of this component
• Added a example project as well to use and added demo screenshots as well

This feature is only done in android. I need some one's help to do it on ios.
Tested on android it works great.

Fixed some of the issues with example as it was not compiling in android
@jedt please check it and merge

[john1jan]

@jedt @theinventor any update on this PR?

[luskin]

Can we get this in?

[john1jan]

@jedt @theinventor can you check this PR

[zerobytes]

Hey @john1jan, I'm thinking that if the default background is transparent, there would be no need to haveall those options of colors. Transparent would suffice, for all cases, once you could just set the background of the wrapping component to whatever you need.

[john1jan]

i have updated the PR please check

[john1jan]

@jedt @theinventor

[jedt]

merged with #216