models: add activeBufferChanged signal

When the active buffer is changed on the model, the model
now emits a signal on the rootScope
ui: scroll to bottom when receiving activeBufferChanged signal

Triggers the ui manipulation code when the rootScope receives the signal.
Supports multiple ways of changing the buffer (clicking, shortcuts, etc.)
without having to duplicate this code.
Remove black foreground colors
Fix wrapping and set all vertical alignment of cells to top
plugins: use  to explicitely trust html
plugins: automatically hide lines that ends with nsfw
plugins: warn the user that content may not be safe for work
plugins: use buttons to display additional content
plugins: let plugins name their content
plugins: provide names for plugins
plugins: fix imagePlugin