Blueprint: Need an `is-active` class for menu-item

[djyde]

When I click a menu item, I want to keep the item looks focused (actived)

[JKillian]

I believe the docs site actually uses something like this, agreed that it would be useful to promote this to the core library

[llorca]

Let's agree on one naming for all these things: .pt-active or .pt-selected?

[adidahiya]

I think we should go with .pt-active to be consistent with how button groups work: http://blueprintjs.com/docs/#components.button-group.css.fill

[leebyp]

Currently the default for .pt-menu-item on hover sets background: @blue3. This means that when using .pt-active on one item and hover over another, it'll look pretty awkward (attached). How about we add something like a .pt-selectable to .pt-menu to change the hover and active state colors to what the docs show right now? (I don't like that name, so open to suggestions) @llorca

[llorca]

Hmm, .pt-selectable doesn't seem necessary. Items are always selectable (unless they're disabled).

Maybe we can simply update the hover state of menus to be gray? @pkwi what do you think?

[leebyp]

I was initially worried about it being troublesome to force the consumer to set the :hover state in the cases where it shouldn't be selectable (eg. in the screenshot). I just realised that's the intention of .pt-intent-primary, so I'm down for the defaults to be like the docs - it also keeps consistency with the default button being grey.