Rename access_token resource

[tobrun]

Been thinking a bit about this and it might be a good idea to rename access_token resource:

<resources>
    <string name="access_token">null</string>
</resources>

to

<resources>
    <string name="mapbox_access_token">null</string>
</resources>

Their is always the possibility that the end user or another library, that the end user is using, is overriding the resource by using resource merging. By prepending mapbox to the key we are making a more unique identifier.

[mb12]

Or we can just add namespace map box to all sdk strings.

<resources>
    <mapbox name="access_token">null</mapbox>
</resources>

[tobrun]

namespace strings are now a supported feature in build.gradle

[tobrun]

[bleege]

This is causing an error when at build time, meaning that it's not possible to build from master right now.

/Users/brad/development/mapbox-gl-android/platform/android/MapboxGLAndroidSDKTestApp/src/main/res/layout/fragment_double_map.xml:11:30-57 : AAPT: No resource found that matches the given name (at 'access_token' with value '@string/mapbox_access_token').

/Users/brad/development/mapbox-gl-android/platform/android/MapboxGLAndroidSDKTestApp/src/main/res/layout/fragment_double_map.xml:25:34-61 : AAPT: No resource found that matches the given name (at 'access_token' with value '@string/mapbox_access_token').

:MapboxGLAndroidSDKTestApp:processReleaseResources FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':MapboxGLAndroidSDKTestApp:processReleaseResources'.
> com.android.ide.common.process.ProcessException: org.gradle.process.internal.ExecException: Process 'command '/usr/local/android/build-tools/23.0.2/aapt'' finished with non-zero exit value 1

[bleege]

The error turned out to be that when running it locally the key in developer-config.xml needed to be renamed from access_token to mapbox_access_token. I've updated the install docs to better communicate this.

[tobrun]

@bleege, I didn't came to mind that others had to remove/regenerate the file (because it's gitignored..). Apologies!