Switch from file mode to block mode with Ctrl+B

[theogf]

Fixes #65

Build a binding to switch from the file selection mode to the block selection based on the currently selected files

[codecov]

Codecov Report

❌ Patch coverage is 0% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.10%. Comparing base (2fba854) to head (e6bdc77).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/testfile.jl	0.00%	15 Missing ⚠️
src/testblock.jl	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #66      +/-   ##
==========================================
- Coverage   47.76%   46.10%   -1.66%     
==========================================
  Files           8        8              
  Lines         335      347      +12     
==========================================
  Hits          160      160              
- Misses        175      187      +12     

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