Share modal template between setting views
Separate admin page logic

Build landing page and settings page separately sharing as much code between
them as possible. In the future it's easier to add more admin pages and still
follow what logic is building which page.
Rename admin pages files.
Use `jetpack_require_lib` for admin pages.
Add trailing blank line
Add translation string.
Added comments
Merge pull request #806 from Automattic/share-modals-between-pages

Separate admin page building logic in Jetpack admin