Single way to generate UUIDs; API for Pouch.uuids

Remove UUID methods from deps/uuids.js which were not being used, but
present from the library. The API to use Pouch.uuids is:

            Math.uuids(count, options)

where options is a object which can be used to change
the UUID format. It accepts:

    length: The length of UUID string
    radix: The base for characters in the UUID

Examples:

>>> Math.uuids()
"92329D39-6F5C-4520-ABFC-AAB64544E172"]

>>> Math.uuids(10, {length: 32, radix: 5})
[ '04422200002240221333300140323100',
  '02304411022101001312440440020110',
  '41432430322114143303343433433030',
  '21234330022303431304443100330401',
  '23044133434242034101422131301213',
  '43142032223224403322031032232041',
  '41121132424023141101403324200330',
  '00341042023103204342124004122342',
  '01001141433040113422403034004214',
  '30221232324132303123433131020020' ]

Signed-off-by: Rohan Jain <crodjer@gmail.com>