[webapi] Rename DLNA to MediaServer

- Rename DLNA to MediaServer

Impacted tests(approved): new 0, update 0, delete 0
Unit test platform: [Tizen IVI]
Unit test result summary: pass 42, fail 16, block 9
Merge pull request #810 from yunxliu/yunxliu/webapi/dlna_rename

[webapi] Rename DLNA to MediaServer