partial response added, new code-style applied
code style fix
string helper fixed, mime-type reverted
Merge PR #275 branch 'partial-response-enh' of https://github.com/Ragazzo/yii2 into Ragazzo-partial-response-enh

* 'partial-response-enh' of https://github.com/Ragazzo/yii2:
  string helper fixed, mime-type reverted
  code style fix
  partial response added, new code-style applied
Display Name of HttpException instead of classname

class name is alwarys HttpException, better display the name of the http
error.
refactored web/Response::sendFile()

- better throw http exception on not satisfiable range request
- constitent header names
- fixed range end when range request is to the end
- added unit test

related to #275, fixes #148
Merge branch 'Ragazzo-partial-response-enh'

* Ragazzo-partial-response-enh:
  refactored web/Response::sendFile()
  Display Name of HttpException instead of classname
  string helper fixed, mime-type reverted
  code style fix
  partial response added, new code-style applied