unsupported watermark functionality

[bbabic]

Current ZencoderWatermark class does not support width & height properties expressed in percentages (Zencoder API allows for % input).

Suggested solution:
a) change int type to String type and thus allow input like "100%"
b) add extra boolean flag to mark value as percent expression. This can be done either as extra getter/setter methods for width and height properties (e.g. setWidthInPercent(123)) or as standalone method (e.g. setIsWidthInPercent(true))