LIMS-2057: Allow custom resolutions for webcams

[ndg63276]

JIRA ticket: LIMS-2057

Summary:

Webcams that don't support 480x270 resolution won't show currently.

Changes:

• Add a config parameter for webcam parameters, supporting resolution and frame rate
• Merge with default parameters before getting webcam stream

To test:

• Add this to your config

$webcamParameters = array(
    'i02-2-webcam04.diamond.ac.uk' => array(
        'resolution' => '640x480',
    ),
);

• Go to an i02-2 visit, eg /dc/visit/cm44135-1, click on "Show i02-2 Webcams & Beamline Status", check 2 webcams are displayed
• Go to /status/bl/i02-2, check 2 webcams are displayed