Extract result histogram chart to its own class

It's hard to see and debug that JS code inside an html file, so
I'm moving it away. Related to #848.
Fix overflow issues with rickshaw

The hover detail popup was going out of the screen when getting closer
to the right screen edge. Updating rickshaw.min.css to 1.4.6 fixed the
issue (somehow it wasn't update on 76c03a8). Related to #848.
Scroll indexer failures table on overflow

The table was taking more space than its container. Until we find a
better solution I'm making it scroll horizontally :/. Related to #848.
Open dropdown menu on the left if there's no space

Check if dropdown menus and submenus can fit on the right side, as they
open usually, and open them to the left if there is not enough space
available. Related to #848.
Add a UI element to unhide sidebar, fixes #701