Make "View the tour again" button less prominent

Per @bpawlak's concerns, make the "View the tour again" button less
attention grabbing relative to the help headers by making it smaller,
using the gray style, and right-aligning it.

Addresses #508
set background color on story viewer modal overlay to dim the background page
Merge branch 'develop' into 519-viewer-modal-overlay
Replace the "View tour again" button with an icon

Replacing the "View tour again" button with an icon makes it compete less with the other help content.  I added a title attribute that will cause "View tour again" to be displayed by the browser on mouseover.

Users might still miss it, so I thought it made sense to show how to view the tour again as part of the tour.

In order to implement the styling of the button, I added a button.reset style (based on the button-reset mixin) that removes the default button styling.  I also layed some groundwork for mixins that match the Font Awesome icon classes.

Finally, I added styles to show the right-facing tour popup arrows, which were missing from the first pass at guider styling.
Merge branch 'develop' into 508-repeat_tour
Update "view tour again" button style

Added text that says "tour" and added our styled tooltips.
correct JS error observed in IE9. possibly related to (caused by) #553. part of fix for #519.
hook into simple modal's open and close callbacks to prevent and re-enable main window scrolling. addresses #519.
update builder header logo with "beta" tag. addresses #488
Factor help action buttons into a separate view
Show asset help icons

The color CSS property had gotten set to white at some point so these icons
weren't showing.
Only show the view tour again button build step

To be forward thinking about this, I conceptualized "help actions" which
could be any kind of buttons that interact with the larger system that are
shown at the top of the content inside the help drawer.

I created a simple API for views in the drawer that have actions associated
with them.  This includes a do:set:helpactions signal that sets a view that
renders and defines UI events for the help actions and a do:clear:
helpactions that removes the view.

I added a HelpView.setActions and HelpView.clearActions method to act as a
handler for the events and a HelpView.renderActions
to break out the call to render the actions view.  This is because I call
setElement to set the element before rendering and in some cases the
this.actionsView isn't set, so the rendering logic is a little more
involved than just calling this.actionsView.render()

Finally, since the view tour again button is no longer shown in steps other
than the build step, I removed the logic that switched to the build step
before showing the tour.

Closes #508
Merge branch '519-viewer-modal-overlay' of https://github.com/patternleaf/atlas into patternleaf-519-viewer-modal-overlay
Merge branch 'develop' of https://github.com/patternleaf/atlas into patternleaf-develop
Increase width of header element

Increase the width of the header element in order to accomodate the wider
image (as a result of the "Beta" text).
Remove help on workflow step switch

When the user navigates away from the build step, the build step help
should be removed from the help view.

I added a do:clear:help event to trigger this and a HelpView.clear method
as a handler for this event.  The do:clear:help event is then fired from
the BuildView.onHide method.

I also updated the help template to include a default message to be shown
if there is no help content set.

Closes #557
Clean up editor toolbar padding
Add "icon" for toggling HTML editing

There's no relevant icon in FontAwesome for editing HTML, so I just used
the characters "HTML".