backgroundStyle prop is usable now to make the backdrop customizable

[WrathChaos]

trafficstars

We cannot customize the backgroundStyle of the tooltip and even we could not hide the backdrop.

Now, we can do it :)

Also solves #169

Example usage:

 <Tooltip
     isVisible={isVisible}
     content={<Text>Check this out!</Text>}
     backgroundStyle={{ backgroundColor: 'transparent' }}>
        <TextInput
              placeholder={emailPlaceholder}
              onChangeText={handleEmailChange}
              autoCapitalize="none"
              {...emailTextInputProps}
         />
</Tooltip>