Add keyboard shortcuts

Add keyboard shortcut through the html `accesskey` attribute :

|Browser	                | Windows	                        | Linux	                                | Mac                                      |  
|-------------------------|--------------------------------------|--------------------------------------|-------------------------------------|
|Internet Explorer	| [Alt] + accesskey	                |  	                                |                                              |
|Chrome	                | [Alt] + accesskey	                | [Alt] + accesskey	                | [Control] [Alt] + accesskey   |
|Firefox	                | [Alt] [Shift] + accesskey 	| [Alt] [Shift] + accesskey 	| [Control] [Alt] + accesskey   |
|Safari	                | [Alt] + accesskey	                |                                         | [Control] [Alt] + accesskey   |
|Opera 15 or newer: | [Alt] + accesskey                 | [Alt] + accesskey                   | [Alt] + accesskey                  |
|Opera 12.1 or older:| [Shift] [Esc] + accesskey     | [Shift] [Esc] + accesskey      | [Shift] [Esc] + accesskey     |


|  Tools                    |Letter | 
|----------------------- |--------|
| WMS Import          | w      |
| KML Import            | k      |
| Compare               | c      |
| Measure                | m      |
| Draw                      | r      |
| Information object  | s      |
| Print                       | p   (with print menu already opened)   |


Test [here](http://mf-geoadmin3.dev.bgdi.ch/dev_shortcut/prod/)