Update flow for signac 1.8.0

[b-butler]

Description

See title. Also updates flow to require at least signac 1.8.0. There will be more breaking changes for 2.0, but we should wait for 2.0 to be released to do that. This also deprecated the usage of alias in flow init while also rendering it effete.

Motivation and Context

To make tests pass and remove deprecation warnings.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• The changes introduced by this pull request are covered by existing or newly introduced tests.
• The package documentation and framework documentation in signac-docs are up to date with these changes.
• I have updated the changelog and added any related issue and pull request numbers for future reference.

[codecov]

Codecov Report

Merging #693 (190d978) into master (95f2af6) will decrease coverage by 0.09%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #693      +/-   ##
==========================================
- Coverage   80.29%   80.19%   -0.10%     
==========================================
  Files          30       30              
  Lines        3136     3136              
  Branches      675      675              
==========================================
- Hits         2518     2515       -3     
- Misses        485      487       +2     
- Partials      133      134       +1     

Impacted Files	Coverage Δ
flow/template.py	80.00% <ø> (-6.67%)	⬇️
flow/__main__.py	82.35% <66.66%> (+0.21%)	⬆️
flow/project.py	82.66% <66.66%> (-0.02%)	⬇️

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