Support for Browser Push in the Java SDK

[mpodwysocki]

Things to consider before you submit the PR:

• [x] Are tests passing locally?
• [x] Are the files formatted correctly?
• [x] Did you add unit tests?
• [x] Did you test your change with either the sample apps that are included in the repository or with a blank app that uses your change?

Description

This adds Browser Push support with the following additions:

• Created per PNS notification classes instead of the Notification class itself
  • AdmNotification
  • AppleNotification
  • BaiduNotification
  • BrowserNotification
  • FcmNotification
  • MpnsNotification
  • WindowsNotification
• Added Browser Credentials and updated the RegistrationDescription
• Added BrowserRegistration and BrowserTemplateRegistration classes to support registrations
• Added BrowserInstallation to differ from regular Installations which have a string device ID versus the BrowserPushChannel
• Added method to save an installation through the BaseInstallation
• Added methods for getting both a regular Installation and BrowserInstallation on the NotificationHubClient

Misc stuff fixed:

• Added JavaDoc to all public members
• Rewrote equals and hashcode implementations based upon IntelliJ recommendations
• Migrated SAS token creation to a single SasTokenProvider

Related PRs or issues

N/A

Misc

N/A