v1.5.0 Release Candidate 1

• login method supports credential parameter (with matching docs and tests updates)
• createFirebaseConnect is now exported at top level (for creating firebaseConnect connected to different store)
• .npmignore expanded to include more files that do not needed to be included in published version (including .babelrc which can cause build errors)
• .babelrc settings are now environment specific (decorators only used in testing)
• babel-preset-stage-1 removed (unnecessary)
• tests folder now has its own .eslintrc which contains globals that are only necessary for testing (simplifies top level eslint config)
• deprecation warning added for token and provider combo in login method
• Docs added for storeAs and keyProp
• firebase is now an external in webpack settings (shrinks build size)