[WIP] Restart after install page

[zeripath]

Currently Gitea will simply try to run normally after the install page has completed. This unfortunately doesn't quite work with duplicate log entries and other problems.

This PR causes Gitea to completely restart after the install page has been run.

Signed-off-by: Andrew Thornton art27@cantab.net

[techknowlogick]

modules\graceful\restart.go:21:10: undefined: originalWD

[codecov-commenter]

Codecov Report

Merging #12696 into master will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master   #12696      +/-   ##
==========================================
- Coverage   43.31%   43.29%   -0.02%     
==========================================
  Files         645      646       +1     
  Lines       71527    71596      +69     
==========================================
+ Hits        30981    30997      +16     
- Misses      35540    35584      +44     
- Partials     5006     5015       +9     

Impacted Files	Coverage Δ
cmd/web.go	0.00% <0.00%> (ø)
modules/graceful/manager.go	27.10% <0.00%> (-1.93%)	⬇️
modules/graceful/manager_unix.go	32.74% <0.00%> (-3.90%)	⬇️
modules/graceful/net_unix.go	18.34% <ø> (ø)
modules/graceful/restart.go	0.00% <0.00%> (ø)
routers/install.go	0.00% <0.00%> (ø)
routers/private/manager_unix.go	0.00% <0.00%> (ø)
modules/util/timer.go	42.85% <0.00%> (-42.86%)	⬇️
modules/sync/unique_queue.go	38.77% <0.00%> (-6.13%)	⬇️
modules/notification/mail/mail.go	34.48% <0.00%> (-3.45%)	⬇️
... and 17 more

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