Change dialog text from params

[khayargoli]

hi @petermetz

I have created this pull request so that users can change the location access dialog box 's title and message by passing params during the installation of your plugin. I see many users wanted this change so I thought I could help with it.

Cordova Usage:
cordova plugin add https://github.com/petermetz/cordova-plugin-ibeacon.git --variable LOCATION_ACCESS_TITLE="This app needs location access" --variable LOCATION_ACCESS_DESCRIPTION="Please grant location access so this app can detect beacons."

Phonegap Usage:
Add these lines to config.xml file of your project:

<plugin name="com.unarin.cordova.beacon" spec="3.8.1" />
        <variable name="LOCATION_ACCESS_TITLE" value="This app needs location access" />
        <variable name="LOCATION_ACCESS_DESCRIPTION" value="Please grant location access so this app can detect beacons." />
</plugin>

Specifying empty LOCATION_ACCESS_TITLE = "" or LOCATION_ACCESS_DESCRIPTION ="" string will use the default title and message.

Thank you