Add additional callback options

[frogen1]

I downloaded source and modified for my application to add a new callback for the handleErase() function.

My project has a touch screen and I needed to give users the ability to erase wifi config without reseting the ESP. This gives them the option to either use the touchscreen or Config/Web portal to set and clear wifi configs.

So I added:

std::function<void()> _erasewificallback;

void WiFiManager::eraseConfigCallback( std::function<void()> func ) {
_erasewificallback = func;
}

And changed the following at the end of:

void WiFiManager::handleErase() {
.......

if (_erasewificallback != NULL) {
#ifdef WM_DEBUG_LEVEL
DEBUG_WM(WM_DEBUG_VERBOSE,F("[CB] _erasewificallback calling"));
#endif
_erasewificallback(); // @callback
}
else if(ret){ //if callback set do not reset. Let callback decide.
delay(2000);
#ifdef WM_DEBUG_LEVEL
DEBUG_WM(F("RESETTING ESP"));
#endif
reboot();
}