scripts: introduce import cleanup using isort

dev_requirements.txt

@@ -6,3 +6,4 b' pytest-localserver < 0.6'
 mock < 3.1
 Sphinx < 1.9
 WebTest < 2.1
+isort == 4.3.21

scripts/whitespacecleanup.sh

@@ -17,4 +17,7 b" sed -i -e 's|^\\([^ /].*,\\)\\([^ ]\\)|\\1 \\2"
 hg mani | xargs chmod -x
 hg loc 'set:!binary()&grep("^#!")&!(**_tmpl.py)&!(**/template**)' | xargs chmod +x
 
+# isort is installed from dev_requirements.txt
+isort --line-width 160 --wrap-length 160 --lines-after-imports 2 `hg loc '*.py'`
+
 hg diff