Add a strip parameter to control EXIF metadata

[lazerg]

Glide never forwards a strip option to Intervention Image, so EXIF handling depends entirely on the driver — GD always drops metadata while Imagick always keeps it, with no way for a caller to control it. This lets the driver config accept an array of options (in addition to the existing driver name string), so strip and other ImageManager options can be set when configuring the server.

Fixes #445

[ADmad]

I don't think allowing strip as an Api (query string) parameter is necessary.

The strip option can be set for the image manager instance too. So we can add it as a ServerFactory option instead and use it when creating the ImageManager instance.

Currently the driver config for ServerFactory can only be a string, we can allow it to be an array too thereby allowing to set other options for the ImageManager also.

[lazerg]

Good call, that's a cleaner place for this. Pushed a commit that drops the strip API param and instead lets driver accept an array so strip (and other ImageManager options) can be set when configuring the server.