Add time slicing

[etheodoridis]

/testbed/2/node/urn:wisebed:ctitestbed:1048576/capability/urn:wisebed:node:capability:battery/fromTime/2011-10-01 17:23:39.0/toTime/2011-10-04 17:23:39.0

return all reading in range for t1<t<t2 slicing

/testbed/2/node/urn:wisebed:ctitestbed:1048576/capability/urn:wisebed:node:capability:battery/fromTime/2011-10-01 17:23:39.0
return all readings after
for t1 <t

/testbed/2/node/urn:wisebed:ctitestbed:1048576/capability/urn:wisebed:node:capability:battery/toTime/2011-10-01 17:23:39.0
return all readings before
for t<t2