Type safety in `gramex.data.[insert|update|delete]`

[jaidevd]

The insert, update and delete functions in gramex.data often tend to fail silently when the args provided are incorrect or incompatible.

E.g.

Suppose x is an int, then doing

gramex.data.filter(**store, args={"col_1", [x]})

returns an empty dataframe if x is not a string, even if col_1 has been designated as an integer column. I guess this is because it's meant for FormHandler HTTP requests.

Here's another example:

gramex.data.delete(**store, args={'xyz': ["1"]})

If xyz is not a column of the table, this line deletes everything in the table.

We should ideally raise TypeErrors and KeyErrors respectively when the user provides wrong args. I'll settle for a warning too.