update to InitOptions type definitions and related API docs

[zacronos]

This PR makes no changes to code, only type definitions and documentation.

Description

It seems the type definitions for InitOptions in types/index.d.ts have gotten a little out of sync with 2.x code changes. This PR updates the type definitions and inline comments for InitOptions to match the current API docs, specifically:

• android.senderID: removed from type definition
• android.clearBadge: added to type definition
• android.messageKey: added to type definition
• android.titleKey: added to type definition
• browser: added to type definition
• browser.pushServiceURL: added to type definition
• browser.applicationServerKey: added to type definition
• ios.senderID: removed from type definition
• ios.voip: added to type definition
• ios.fcmSandbox: updated inline comments to match API docs (old comments referenced GCM and obsolete ios.senderID field)

This PR also makes some minor changes to the API docs for formatting consistency, plus a typo fix.

Motivation and Context

Without the type definition changes, TypeScript IDEs will flag errors on perfectly valid options passed to PushNotification.init().

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[fredgalvao]

That's awesome, thanks for helping keep it in sync!

[lock]

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