Add Dismissible state to Flash component

[blazebarsamian]

Broken out from #415

I'm submitting a ...

• bug report
• feature request
• support request

What is the current behavior?
Currently there is a prop thats being created in this PR (#417) for a dismissible flash message. However some work needs to be done to this component by an engineer to make sure its written properly and functions as intended.

What is the expected behavior?

• When a dismissible flash (<Flash dismissible> is used
• Then I can click the close button and the flash will no longer be visible.

When writing this component:

• I would like for the close button component to be included inside the flash component itself so that when youre using it all you have to write is <Flash dismissible> Dismissible flash message </Flash and the close button will be included.
• Harmonium doesnt have icons working so well need to use x or - for the close button for now.
  • HOWEVER, we should make it so that users could easily plug in different icons to be used as the close button (most likely using the icon component)

For feature requests: why should the behavior change?
Because we use a dismissible flash message on most projects and so it would be nice to have a component that we can pull from and use instead of reinventing the wheel every time.

[Dacello]

@blazebarsamian im gonna pick this up and just branch off of #417. Ill make a PR into that

[Dacello]

@blazebarsamian FYI this was merged into #417 -- would you mind taking another look at that PR to see if it can be merged?