Added --help option to standalone-server

Here's how it looks at the moment!

```
################# Selendroid #################
Usage: Selendroid Standalone Server [options]
  Options:
    -h, --help
       Prints usage instructions to the terminal
       Default: false
    -app, -aut
       location of the application under test. Absolute path to the apk
       Default: []
    -deviceLog
       Specifies whether or not adb logging should be enabled for the device
       running the test
       Default: true
    -deviceScreenshot
       if true, screenshots will be taken on the device instead of using the
       ddmlib libary.
       Default: false
    -emulatorOptions
       The emulator options used for starting emulators: e.g. -no-audio
    -emulatorPort
       port number to start running emulators on
       Default: 5560
    -forceReinstall
       Forces Selendroid Server and the app under test to be reinstalled (for
       Selendroid developers)
       Default: false
    -host
       host of the node. Ip address needs to be specified for registering to a
       grid hub (guessing can be wrong complex).
    -hub
       if specified, will send a registration request to the given url. Example
       : http://localhost:4444/grid/register
    -keepAdbAlive
       If true, adb will not be terminated on server shutdown.
       Default: false
    -keystore
       The file of the keystore to be used
    -keystoreAlias
       The alias of the keystore to be used
    -keystorePassword
       The password for the keystore to be used
    -logLevel
       Specifies the log level of selendroid. Available values are: ERROR,
       WARNING, INFO, DEBUG and VERBOSE.
       Default: ERROR
    -noClearData
       When you quit the app, shell pm clear will not be called with this option
       specified.
       Default: false
    -noWebviewApp
       If you don't want selendroid to auto-extract and have 'AndroidDriver'
       (webview only app) available.
       Default: false
    -port
       port the server will listen on.
       Default: 4444
    -proxy
       if specified, will specify the remote proxy to use on the grid. Example :
       io.selendroid.grid.SelendroidSessionProxy
    -selendroidServerPort
       the port the selendroid-standalone is using to communicate with
       instrumentation server
       Default: 8080
    -serverStartTimeout
       Maximum time in milliseconds to wait for the selendroid-server to come up
       on the device
       Default: 20000
    -sessionTimeout
       maximum session duration in seconds. Session will be forcefully
       terminated if it takes longer.
       Default: 1800
    -timeoutEmulatorStart
       timeout that will be used to start Android emulators
       Default: 300000
    -verbose
       Debug mode
       Default: false
```