Change define constants Name and Version with file data

[EkoJR]

Issue #2926

Proposed changes

Refactors how constants AIOSEOP_VERSION & AIOSEOP_PLUGIN_NAME are defined by using a WP function get_file_data() to retrieve plugin details from the file header.

This would eliminate having to edit the version number in more than one area, and isolates changes to the file header.

Types of changes

What types of changes does your code introduce?

• Improves existing functionality
• Improves existing code

Checklist

• [x] I've selected the appropriate branch (ie x.y rather than master).
• [x] I've created an appropriate title, descriptive of what the PR does.
• [x] Travis-ci runs with no errors.

Testing instructions

Areas to check version number (& plugin name).

• General Settings page on the right side bar there should be a version number.
• Welcome page should also show a version number.
• Inspect Source on admin side should have scripts loaded with a version number ?v=3.2.1.

Further comments

AIOSEOP_PLUGIN_NAME was included since data was already available and eliminates having to conditionally define the constant.

[arnaudbroes]

This is good and can be code reviewed.

I've done a code review as well and it looks good. One comment for @EkoJR is that this should be moved to the Core class https://github.com/semperfiwebdesign/all-in-one-seo-pack/pull/3045 introduces as soon as this is merged.