Add an info popup and zoom buttons

[IanButterworth]

See the new i icon here.

I wanted to add a colored legend too, but the flamegraph colors are dynamic, and showing colors in a gtk popup would take some work.

[codecov]

Codecov Report

Merging #188 (e2b7fa5) into master (c048a49) will decrease coverage by 2.56%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #188      +/-   ##
==========================================
- Coverage   80.99%   78.43%   -2.57%     
==========================================
  Files           2        2              
  Lines         221      255      +34     
==========================================
+ Hits          179      200      +21     
- Misses         42       55      +13     

Impacted Files	Coverage Δ
src/ProfileView.jl	84.74% <66.66%> (-3.87%)	⬇️

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[IanButterworth]

I tried to add a test for this, but I can't find a way to programmatically close a Gtk.info_dialog given that the function doesn't return until the user clicks "OK". A timed async destroy might have worked, but felt a bit ugly for testing

[IanButterworth]

Also added:

• Zoom buttons
• Toolbar spacers
• Tooltips on the toolbar buttons

[timholy]

Amazing! Big step forward for usability.

Too bad about the difficulty of running the test. It would be nice if we could couple the Close button to an Observable, but that can be separate. We should merge this without the test since I think it's a strict improvement.

[timholy]

Merge when ready, and tag a new release.