Fix bugs and make improvements relevant to temporary credentials request

OAuth header from ParameterList: add spaces in the beginning of line, remove extra comma in end, percent encode name=value pairs
Text signature: secrets should be separated by ampersand, not question mark
HMAC_SHA1 signature should not be encoded in hmacSha1Signature, it'l be encoded when ParameterList will be converted to header
Add parameters without decoding of percent encoding, where decoding isn't required
Fix token constructor call in getRequestToken
Fix signature tests according to changes
this commit fixes #17