Remove BlankRawContact entity

[vestrel00]

Problem

Due to the changes in #268, it no longer makes sense to keep the BlankRawContact entity. The main purpose of the BlankRawContact in conjunction with the AccountsRawContactsQuery was to provide users a way to get a list of RawContacts and their display name and account, all of which are now a part of the regular RawContact entity.

Solution

• Delete BlankRawContact and replace references with RawContact
• Delete ExistingRawContactEntityWithContactId and replace references with ExistingRawContactEntity

Additionally;

• Update sample app
• Update cheatsheet (also move to basics section)
• Update relevant documentation in code
• Verify that there are no regressions for related API functions
• Provide a migration guide as a comment in this issue so that it can be copy-pasted into the release notes

[vestrel00]

Migration guide (to be included in release notes)

Now that BlankRawContact no longer exists, all you have to do is replace any references you may have to it with references to RawContact.

[vestrel00]

This is included in 0.3.0!