Rework WP_App Interface

[josesimoes]

Description

• Remove duplicated code on all platforms.
• Rename function to improve code reuse in nanoBooter and nanoCLR.

Motivation and Context

• Following DRY principle. Making easy to add new platforms.

How Has This Been Tested?

Screenshots

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Config and build (change in the configuration and build system, has no impact on code or features)
• Dependencies (update dependencies and changes associated, has no impact on code or features)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[nfbot]

@josesimoes there are issues with the code style on the source files.
A PR was submitted with the code style fixes. Please review and merge the changes. See Eclo#66.

Make sure you are using the project code style. Check the details here.