Syncbase Watch: make watch set more flexible

[ivanpi-mtv]

Watch currently supports watching a single prefix in a single table.

Improvement proposals:

• use RowRange, making it more similar to Scan, possibly with special support for single row (Syncbase Feature request for RowRange to Watch #852)
• multiple tables and RowRanges in a single call
• table name patterns/prefixes (e.g. watch entire database)
• watch by query (at least where clause predicates, possibly projection and order within batch as well), to make Exec followed by Watch more seamless

Also see #906

@kenashcraft (syncslides), @jxson (reader), @AsturaPhoenix

[aghassemi]

+1 for watching entire database.

[ivanpi-mtv]

Related: #1264 (except watch by query)

[ivanpi-mtv]

Implemented watching multiple patterns over collections and keys in v.io/c/22284 . Watch by query is lower priority.