Additions to the Starxpand Flutter

[ro0t]

Added some new functionality to the starxpand_flutter package.
The following additions were only made to the Flutter models and Android folder. We do not use iOS devices right now so we did not spend time on it.

• Added Display screen capability (If a display screen is connected to another Star Micronics printer)
• Added GetStatus to get a detailed status for the printer (If the paper is empty, near empty, drawers are open, ..etc)
• Added getActions() on the PrintDocument for Unit testing in our project.
• Increased version to 0.1.5
• Increased stario library version
• Updated gradle version

Let me know if I need to make some changes for it to be added to the main package.