toobarSelect replaces toolbar when rows are selected

I'm not sure if it's bug or not, but it is negative user experience.

If you select any rows after applying search of filters, toolbarSelect (which shows how many rows you are selected) replaces and hovers standard toolbar, thus make it impossible to discard or change search, or change filters (but you can discard filters, as they appear under toolbar).

So, if user select any rows after searching, he must discard his selection first to discard or change search string, making it useless to search and then select rows.

## Expected Behavior

After selecting rows, user can change search string of filters.

## Current Behavior

After selecting rows, toolbar disappears (replaced with toolbar select)

## Steps to Reproduce (for bugs)

1. Search smth in your table.
2. Select any of found rows.

## Your Environment

| Tech | Version |
|--------------|---------|
| Material-UI | 3.3.1 |
| MUI-datatables | 2.0.0-beta-52 |
| React | 16.6.0 |
| browser | chrome |