Add Milwaukee themes (#191)

Milwaukee has an active Slack community and these color schemes are based on [the new Milwaukee flag](https://milwaukeeflag.com/).

data/themes.yml

@@ -40,6 +40,9 @@
 - { colors: '#40364D,#312a3c,#312A3C,#F58D8C,#312A3C,#a097ad,#F58D8C,#F58D8C', name: 'Kayako Minimal' }
 - { colors: '#F56262,#F56262,#424242,#F5F5F5,#ed5151,#F5F5F5,#F5F5F5,#424242', name: 'Laravel' }
 - { colors: '#FAFAFA,#FB503B,#FB503B,#FFFFFF,#F58F82,#1C1B1C,#FB503B,#424242', name: 'Laravel Light' }
+- { colors: '#0D2240,#00A8E1,#F7A800,#FFFFFF,#00A8E1,#FFFFFF,#00A8E1,#00A8E1', name: 'Milwaukee Dark' }
+- { colors: '#00A8E1,#0D2240,#F7A800,#FFFFFF,#0D2240,#FFFFFF,#F7A800,#0D2240', name: 'Milwaukee Mid' }
+- { colors: '#FFFFFF,#00A8E1,#0D2240,#FFFFFF,#F7A800,#0D2240,#F7A800,#00A8E1', name: 'Milwaukee Light' }
 - { colors: '#212420,#333632,#87CF3E,#FFFFFF,#393d39,#FFFFFF,#87CF3E,#68a030', name: 'Mint' }
 - { colors: '#222222,#2F2F2F,#F92772,#FFFFFF,#A6E22D,#FFFFFF,#66D9EF,#BE84F2', name: 'Monokai' }
 - { colors: '#0D7E83,#076570,#F79F66,#FFFFFF,#D37C71,#FFFFFF,#F79F66,#F15340', name: 'Monument' }