Issue #2845486 by Jo Fitzgerald, quietone, gaurav.kapoor, ohthehugemanatee, heddn, Yogesh Pawar, catch, shabana.navas, phenaproxima, mikeryan: Rename Migration process plugin and add documentation

Issue #2543568 by mikeryan, quietone, Ryan Weal, chipway, iMiksu, heddn, alexpott: Remove the md_entity destination plugin hack

Revert "Issue #2560795 by mikeryan, phenaproxima, penyaskito, willwh, benjy: Source plugins have a hidden dependency on migrate_drupal"

This reverts commit 89815ba3.

Issue #2560795 by mikeryan, phenaproxima, penyaskito, willwh, benjy: Source plugins have a hidden dependency on migrate_drupal

Issue #2463909 by phenaproxima, mikeryan: Migrations should support non-installed default configurations (templates)

Issue #2460529 by alexpott, chx, phenaproxima: Migrations need to use the configuration entity dependency system

Issue #2466797 by mikeryan, benjy: Rename migration_groups key to avoid confusion with MigrationGroup support

Issue #1847596 by amateescu, amitaibu, YesCT, Berdir, David_Rothstein, xjm, rteijeiro, ParisLiakos, webchick, Wim Leers, yched, jhodgdon, Bojhan: Remove Taxonomy term reference field in favor of Entity reference

Issue #2287727 by yched, swentel, alexpott: Rename Field[instance]Config classes and entity types (again).

Issue #2293773 by Gábor Hojtsy, alexpott, penyaskito: Fixed migrations use dots in key names - not allowed in config.

Issue #2121299 by andypost, bdone, benjy, penyaskito, chx, claudiu.cristea, damiankloip, gregboggs, InternetDevels, jessehs, jhedstrom, marvil07, mikeryan, pcambra, Xano, YesCT, axoplasm, kgoel, dclavain, jeckman, alvar0hurtad0, Drupali, fastangel, gloob, jhedstrom, joshtaylor, mpgeek, alexpott: Migrate Drupal 6 to Drupal 8