Fix refresh! on Windows

[davidanthoff]

On Windows up and down and erase_line don't position the cursor at the beginning of the line, so that new output is rendered incorrectly. By using prev_line and next_line that is fixed.

Also changed the semantics of replace_line so that it doesn't move the cursor to the next line, that makes things a bit easier.

Next testing this on Mac.

This fixes some of the problems on Windows, but not all of them.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.13%. Comparing base (440ce2c) to head (9e8f769).
⚠️ Report is 20 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Live/app.jl	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #265      +/-   ##
==========================================
+ Coverage   87.27%   88.13%   +0.86%     
==========================================
  Files          48       48              
  Lines        2899     2908       +9     
==========================================
+ Hits         2530     2563      +33     
+ Misses        369      345      -24     

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