Add support for Polycom phone pagination feature

Poly supports pagination on their VVX 250 & VVX 350 models, which allows the activation of presence button pages. This would support a few pages of presence soft buttons without the need for an expansion module. While pagination can be activated locally on the phone it isn't functional without RingCentral writing additional presence lines into the configuration file. Additional presence lines should be added to the configuration file regardless of whether pagination is enabled, since the phone will still only show the number available and ignore those not supported- this change would allow companies to enable pagination on their phones and take advantage of the feature if they are inclined though. With the two self line minimum it reduces the available presence lines severely, but this would help to offset it.