ePMV all: make [√] Surface-per-chain an option next to MSMS and CMS in GUI?

[gj210]

Surface-per-chain is one of the most used scripts... I wonder if we should consider upgrading it a GUI button- could be one button on the MSMS line and one on the CMS line, or it could be a checkbox option for MSMS and CMS, i.e. surface the current selection as one object or surface the current selection per chain- we can talk about that in the future.... although it is nice to encourage people to to use the scripting interface, this one may be too nice to "hide" since so many people are scared by scripting.