Initial GridView Implementation

[jvalkeal]

We need a layouts not just "view" components. Layout would also be a view but having more dedicated role to layout views it knows about into its own bounding box.

GridView would be a port from https://github.com/rivo/tview/blob/master/grid.go as it has some nice ideas without making implementation too complex while still providing enough features.

Every "box" in a grid is a view which allows user to build these type of views by composing a layout.

┌─────────────────────────────────────────────────────────────┐
│                          Header                             │
│                                                             │
├────────────────┬─────────────────────────┬──────────────────┤
│      Menu      │      Main content       │     Side Bar     │
│                │                         │                  │
│                │                         │                  │
│                │                         │                  │
├────────────────┴─────────────────────────┴──────────────────┤
│                          Footer                             │
│                                                             │
└─────────────────────────────────────────────────────────────┘

• Can add items
• Can set column sizes
• Can set row sizes
• Can set minimum sizes for rows and columns