Fix the RLMVerifyInWriteTransaction error message

Closes #1094.
Added GroupedTableView examples for Objective-C and Swift
simplified tableview examples
Added GroupedTableView example entries in examples/README.md
Merge pull request #1106 from realm/jp-grouped-tableview

add sections to table view examples
Merge pull request #1098 from realm/tg-write-error

Fix the RLMVerifyInWriteTransaction error message
Add -[RLMRealm writeCopyToPath:]

We've had a few requests for this functionality pop up and there's no reason
not to expose it.
Merge pull request #1091 from realm/tg-save-copy

Add -[RLMRealm saveCopyToPath:]
added test to confirm that writing to two different realms simultaneously works
Merge pull request #1121 from realm/jp-multiple-realm-test

added test to confirm that writing to two different realms simultaneously works
Add support for encrypted Realms