Option `setDimensions` to allow deactivation of inline widths and heights at player elements

Currently the setting of widths and heights to the player is somehow broken, as one can't set values of `100%`.

I favor to set widths and heights for multiple players via CSS (and using media queries) instead of setting them later via JS. I've added the option `setDimensions` which has a default value of `true`. One may set this option to `false` to disable any inline styles for widths and heights.

commit message: “mep-player.js: add option (setDimensions) to disable the setting of widths and heights through JS, since there was no way to have a fluid player width and height (i.e. set to 100% each)”