Refactor aiohttp-debugtoolbar to use new aiohttp sub application

[jettify]

• Create separate app for aiohttp-debugtoolbar
• Hide all toolbar related URL behind this sub app

See also #65

[samuelcolvin]

Any progress on this?

Currently aiohttp-debugtoolbar is more or less unusable with sub apps AFAIK. Or is there a workaround I'm missing?

Even if DBTB doesn't support sub-apps completely it shouldn't completely break when they are used, see aio-libs/aiohttp-devtools#39.

[jettify]

Toolbar had been crated long before aiohttp introduced subapp feature, this improvement is more about proper code plug in, then functionality. I don not have any ETA for this, but PR is welcome

[Dreamsorcerer]

Once this is done, we can also switch jinja templates to use static() for URLs (see #478).