Change "Manage display" and "Manage form display" to be consistent with the idea of "Display modes"

Problem/Motivation

In an effort to make the admin UI as consistent as possible, I propose that we change "Manage display" and "Manage form display" to "Manage view modes" and "Manage form modes". This will make it more consistent with Display modes in Drupal 8.

Proposed resolution

Change the labels on the tabs and the pages.

Remaining tasks

User interface changes

API changes

Data model changes