Add translation en_CA

[Hb---]

Please enable en_CA to be delivered with JOSM. All strings are translated as of today.

The Canadian translation is only a dialect of the source. It wants to deliver a terminology as distinguishable as possible. It prefers to:

1. Bind a verb exclusively to a noun or an action.
   • While the source uses "to select" for objects, menu items, list entries, files, checkbox states, download areas and nearly everything else the dialect tries to bind this verb to the meaning of selecting map objects for the Selection.
     The dialect
     chooses menu items, list entries, data sets and files
     checks checkbox states and
     defines download areas.
     Additionally the dialect goes even further and often replaces the term the selected objects by the proper noun the Selection. With this noun the Canadians want to honor the superior importance of these hand-picked elements in JOSM.
     
     
   • The source uses "to move" for objects, tags and for the map view but the dialect limits this to to moves objects only and
     pans the map and
     shifts tags from ways to relation for example.
     
     
   • The source uses "to toggle" for dialog panels, some states of the GUI and map data. But the dialect limits this to toggled by TAB keystroke effects and uses hide/show for other means of visibility switching.

2. Limit the amount of work needed for the two source strings Do not hide toolbar and Do not hide status bar by simply using only one translation for both them: Do not toggle this bar by TAB key. Perhaps the lazy Canadians are going to use this translation for Do not hide toolbar and menu too.

3. Honor the importance of the Working mode in JOSM.
   • When the Canadians see a mode they are not stingy with words and call it a mode. For example:
     Select mode - Select, move, scale and rotate objects instead of Select, move, scale and rotate objects
     Extrude mode - Create areas, move way segments instead of Create areas
     Zoom mode - Zoom and pan map instaed of Zoom and pan map
     
     
   • But when the people south of their border want them to call something a mode what clearly is not a mode the Canadians get angry and use their dialect to say
     Expert view instead of Export mode.

4. Harmonize the names of the subpages of the Preferences dialog to <name> preferences instead of <name> [settings|customization|Preferences|].

5. Avoid SPACE and three dots in their menus if these characters are not needed. So they use
   Undo instead of Undo... and
   Redo instead of Redo... because these commands acts without a following dialog.
   Downloading open changesets... because not SPACEis needed in front of the dots.

Feel free to hear from the friendly Canadians.