Add header with navigation

[argemiront]

Add navigation buttons in a header as:

• Home (first page)
• Back / Forward
• Task list

[ShMcK]

One issue with adding a header:

New -> Select Tutorial -> Overview -> Level
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If a user creates a "new" tutorial, git init is run and files are loaded in the workspace.

Once a user hits "start" on the "Overview" page, there is no going back unless they open a new project workspace. Otherwise we would have to delete all of a users git and files, which may be problematic, especially if run in the wrong folder. There are many dangers in running rm -rf .* && rm -rf * to clear the files.

We can and should, however, add a back button from Overview -> Select Tutorial

We could allow users to exit from the Level view if it opened a new folder and launched CodeRoad in that folder. That might be a bit complicated at this time.

[ShMcK]

I've added a back button on the summary page. UI needs some work, but functionality is there for now.