Remove box-shadow from UI, fix dashboard issue

[silverwind]

Two tweaks here:

1. Remove box-shadow from menus and segments. I think it generally looks better this way because most of the UI elements are already flat, and the box-shadowed elements look out-of-place.

Before

After

2. Fix a issue where the repo list in the dashboard sidebar was 2px wider than the pill menu above it. The cause of the issue looks to be some hacks in Semantic UI and that added artificial width to that repo box.

Before

After

[silverwind]

Fun fact: gogs has done a similar change on hiding the box-shadows. I just went ahead and adopted the change as it seemed cleaner.

[codecov-io]

Codecov Report

Merging #3065 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3065      +/-   ##
==========================================
- Coverage   33.45%   33.42%   -0.04%     
==========================================
  Files         270      270              
  Lines       39553    39553              
==========================================
- Hits        13232    13219      -13     
- Misses      24429    24445      +16     
+ Partials     1892     1889       -3

Impacted Files	Coverage Δ
models/repo_indexer.go	45.54% <0%> (-6.44%)	⬇️
modules/indexer/repo.go	60.86% <0%> (-2.61%)	⬇️
modules/process/manager.go	81.15% <0%> (+4.34%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ef53649...10297f2. Read the comment docs.

[lafriks]

LGTM

[ethantkoenig]

LGTM

[lafriks]

@silverwind please resolve conflicts

[silverwind]

Rebased.

[lafriks]

Can you please force push?

[silverwind]

done