add arguments in StartAppRequest

[knorth55]

UPDATED:

I want to add arguments in StartAppRequest service.
in this PR, I use app_manager/KeyValue message to pass arguments.

$ rossrv show app_manager/StartApp
string name
app_manager/KeyValue[] args
  string key
  string value
---
bool started
int32 error_code
string message
string namespace

[knorth55]

UPDATE:

I switch to use app_manager/KeyValue message to pass arguments.

$ rossrv show app_manager/StartApp
string name
app_manager/KeyValue[] args
  string key
  string value
---
bool started
int32 error_code
string message
string namespace

[k-okada]

@knorth55 Could you update document too ? I found

$ rosservice call /robot/start_app app_manager/appA

in https://github.com/PR2/app_manager/blob/kinetic-devel/README.md#examples did not work