Make eventSource use timeout for reconnect

[runeharlyk]

Purpose

• When the ESP is temporarily disconnected, the frontend tries to reconnect every 2000 ms. This means when the ESP becomes online again, all those connections become active.
• The hot reloading creates new connection as the unresponsive timeout is not cleared.

Description

By changing the EventSource reconnect to use a timeout instead of a interval and clearing the unresponsive timeout at disconnect only one connection will be active at a given moment.

[theelims]

Thank you so much for this contribution.