Support SQL views

[hatyo]

This can be thought of as a succession of #3282, with focus on supporting SQL views in the schema template definition:

create schema template myTemplate
create table t1(col1 integer, col2 string, primary key (col1))
create view v1 as select * from t1 where col1 < 200

Similar to table-valued functions, the view definition is saved in the metadata, and its expansion is amortized:

select * from v1;

later on, we should also support the creation and deletion of transaction-based temporary views, similar to temporary functions, for completeness.