Add clear flapping functionality

[podliashanyk]

Closes #66

Implemented changes:

• Selected events are now stored as dict in session in order to keep info about type of selected events. This is because clear flapping functionality is only applicable to portstate events. Therefore clear flapping button in bulk menu is shown only if all selected events are of type portstate.
• Enabled clear flapping button in detailed event view for portstate events.
• Removed clear flapping button from detailed event view for events that are not portstate.

[github-actions]

Test results

  4 files    4 suites   8s ⏱️
14 tests 14 ✔️ 0 💤 0 ❌
56 runs  56 ✔️ 0 💤 0 ❌

Results for commit f77209c.

♻️ This comment has been updated with latest results.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 16.07143% with 47 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@0f25da1). Learn more about missing BASE report.

Files	Patch %	Lines
src/howitz/endpoints.py	16.07%	47 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #85   +/-   ##
=======================================
  Coverage        ?   47.30%           
=======================================
  Files           ?       15           
  Lines           ?      890           
  Branches        ?        0           
=======================================
  Hits            ?      421           
  Misses          ?      469           
  Partials        ?        0           

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[hmpf]

Just some python syntax nitpicks this time around.

[lunkwill42]

Looks ok to me. Works as long as I merge with main first...