test: added backrunner test subsystem
btest/elliptics: reduce number of various elliptics server threads
test/btest: added delete/bulk-delete test
bucket: added size/offset URI parsing into Stream method
test: added correctness check of the uploaded/downloaded content
bucket: added offset/size URI params to all upload/get handlers
proxy: use decoded uri (i.e. for example in russian) for keys
test: added utf8 uri into upload/download test