Introduce position column on ObjectMetadata

[FelixMalfait]

• add a column position on ObjectMetadata to determine if it should be displayed on the app's left menu and its position (null = not displayed)
• create a decorator for menu position, initialize people/companies/opportunities with big numbers to leave room in the future (e.g. 1000000 200000 300000), make sure it's properly initialized for custom objects (added at the end)

[FelixMalfait]

(the primary goal of this is to decorrelate visibility of an object in the app and visibility in settings, it'd be useful to expose some objects in settings without having them appearing automatically on the sidebar)

[FelixMalfait]

Marking as blocked as I feel the separation could also depend on the Layout, depending on our strategy to implement layouts

[FelixMalfait]

Instead we we'll use Favorites to decorelate menu from objects. Not all objects will be displayed in the menu