Update version number to 0.6.0

[jmgrady]

Set version to 0.6.0 to include the following PRs:

• Refactor temporary files generated by backend (Refactor temporary files generated by backend #810)
• Add liftImported field to existing projects (Add liftImported field to existing projects #815)
• ExportProject actions/reducer/state (ExportProject actions/reducer/state #812)
• Add Markdown link to Docker deployment docs (Add Markdown link to Docker deployment docs #816)
• Centralize the AppBar; Remove extraneous component wrappers (Centralize the AppBar; Remove extraneous component wrappers #807)
• Remove GC.Collect() call that did not have any noticeable improvement for memory usage (Remove GC.Collect() call from Lift Export #813)
• Add explicit default formatters by language (Add explicit default formatters by language #808)
• Set cache expiration so that if the server's frontend implementation is updated (Set cache expiration for frontend route #809)
• NewEntry note (NewEntry note #802)
• Consolidate navigation paths; Cleanup GoalTimeline folder structure (Consolidate navigation paths; Cleanup GoalTimeline folder structure #805)
• [Login, UserManagement] Avoid avatar 404 error ([Login, UserManagement] Avoid avatar 404 error #797)
• Modify TreeView search's event handler to preempt material-table's (Modify TreeView search's event handler to preempt material-table's #804)
• Project export filename projectName_date_time (Project export filename projectName_date_time #800)
• Force garbage collection at end of ExportLiftFile() (Force garbage collection at end of ExportLiftFile() #801)
• [NewEntry] Allow submission with no gloss ([NewEntry] Allow submission with no gloss #796)
• Add download attribute to export tag (Add download attribute to export <a> tag #799)

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This change is 

[codecov-io]

Codecov Report

Merging #818 (7a642c0) into master (d7cf58f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #818   +/-   ##
=======================================
  Coverage   51.26%   51.26%           
=======================================
  Files         239      239           
  Lines        6505     6505           
  Branches      420      420           
=======================================
  Hits         3335     3335           
  Misses       2860     2860           
  Partials      310      310           

Flag	Coverage Δ
backend	55.68% <ø> (ø)
frontend	47.03% <ø> (ø)

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[imnasnainaec]

Reviewed 2 of 2 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved