Add AdminEntry type and fix small declaration file errors.

[OrmEmbaar]

PR contains the following:

1. Add AdminEntry type for the entries field on AdminBlock.
2. Allow mixed type args for AdminBlock.getEntriesOfTypes (previously the Typescript compiler would enforce a single type across all args).
3. Add an AdminCode enum for use in the AdminEntry type and as an input into AdminBlock.getEntriesOfTypes.
4. Make timestamp and blockContext fields optional on the Entry type (necessary for getEntry method).