MapView shapshot and show all markers

Added two scriptclass functions, snapshot for taking an image of the current MapView display and showAllMarkers to zoom MapView to the particular position where all of the markers is visible on the MapView

Examples:

<App>
    <ClientPanel>
        <JavaScript>
            var Observable = require('FuseJS/Observable')
            var snapshotImage = new Observable()
            var Map = map;
            module.exports = {
                snapshotImage,
                showAllMarkers: function(args) {
                    Map.showAllMarkers();
                },
                takeSnapshot: function(args) {
                    Map.snapshot().then(function (path) {
                        snapshotImage.value = path;
                    })
                }
            };
        </JavaScript>
        <DockLayout />
        <NativeViewHost Dock="Top" Height="250">
            <MapView ux:Name="map" Zoom="14" Latitude="-6.914742" Longitude="107.609820">
                <MapMarker Latitude="-6.914742" Longitude="107.609820" />
                <MapMarker Latitude="-6.915850" Longitude="107.609929" />
                <MapMarker Latitude="-6.916959" Longitude="107.619009" />
            </MapView>
        </NativeViewHost>
        <Panel>
            <StackPanel ux:Name="stack" ItemSpacing="10" Orientation="Vertical">
                <Button Text="Show Markers" Clicked="{showAllMarkers}" />
                <Button Text="Snapshot" Clicked="{takeSnapshot}" />
            </StackPanel>
        </Panel>
        <Panel Dock="Bottom">
            <StackPanel ux:Name="a" ItemSpacing="10" Orientation="Vertical">
                <Image Size="200" File="{snapshotImage}" StretchMode="Uniform" />
                <Text Value="{snapshotImage}" />
            </StackPanel>
        </Panel>
    </ClientPanel>
</App>

This PR contains:

[x] Changelog
[x] Documentation
[ ] Tests

fuse-open / fuselibs

MapView shapshot and show all markers #1395