Client side filtering when serverSide option set to 'true'

## Expected Behavior

As a suggestion for an improvement, the expected behavior would be that the table be configurable to provide an option as to whether behaviors such as searching or filtering data take place at the client's end, even if the `serverSide` flag is set to true.

## Current Behavior

Presently, when the `serverSide` flag is set to true in the table options object, it expects all the associated functionalities (E.g. - Searching the table, filtering the data, etc) to be handled remotely, i.e, by the server. This was as a result of a fix pertaining to a prior issue raised in this repository ([#414](https://github.com/gregnb/mui-datatables/issues/414)) . I do not aim to revert this change, rather I would like to suggest that this behavior be made customizable, and we can still choose to have the filtering done by the client even when this flag is enabled. The fix for #414 did not provide such an option.

## Your Environment

| Tech | Version |
|--------------|---------|
| Material-UI | 4.11.0 |
| MUI-datatables | 3.4.1 |
| React | 16.12.0 |
| browser | Chrome |

Start by reviewing the table options and the serverSide behavior described in issue #414. Trace how searching and filtering are delegated when serverSide is true, then determine how a configurable client-side path could coexist with the existing behavior. Done means the option supports client-side searching and filtering without reverting server-side handling.

Written by the indexing model from the issue text.