Minor fixes to Search tool

[offtherailz]

Description

• [x] Placeholder doesn't show anymore 2020.01.01 2020.02.00

• [x] componentDidMount of search pluginis called frequently, triggering the action updateResultsStyle on everyAction.

How to reproduce

• open a map and open dev tools in debug mode

• Interact with the map to see this continuous triggering of this action.

• [x] Not browser related

Browser info

(use this site: https://www.whatsmybrowser.org/ for non expert users) | Browser Affected | Version | |---|---| |Internet Explorer| | |Edge| | |Chrome| | |Firefox| | |Safari| |

Other useful information

[tdipisa]

@offtherailz it seems working now, can we close this?

[offtherailz]

Yes, it is a duplicate of https://github.com/geosolutions-it/MapStore2/issues/5200. I solved the componentDidMount in this PR https://github.com/geosolutions-it/MapStore2/pull/5061