Merge branch 'remove-chart' into 'master'

Only load Chart.js when necessary.

Only load Chart.js where it's used, namely the Graphs section. Follow up on !4394.

cc: @jschatz1 

See merge request !4516

app/assets/javascripts/application.js.coffee

@@ -35,7 +35,6 @@
 #= require raphael
 #= require g.raphael
 #= require g.bar
-#= require Chart
 #= require branch-graph
 #= require ace/ace
 #= require ace/ext-searchbox

app/assets/javascripts/graphs/application.js.coffee

@@ -4,4 +4,5 @@
 # It's not advisable to add code directly here, but if you do, it'll appear at the bottom of the
 # the compiled file.
 #
+#= require Chart
 #= require_tree .