Global Templating + Last Partition Templating

[czgu]

Add the ability for the user to define templating for themselves, when running queries, the owner's custom definition will be taken into consideration. These templates need to be able to be represented in text form for ease of sharing with others.

Add get the latest table partition for hive metastore and provide a default function that lets the user get the latest partition of a table via a function call. The signature should be something like

lastest_partition(table_name, pattern=None,)

All available functions and variables should be available to view/update somewhere near the query editor UI.

[czgu]