Ensure entity key only exists once in the entitylist

[groovecoder]

While processing the entity list, ensure that each property & resource domain only occurs in a single entity, to prevent down-stream bugs where a duplicate resource domain might be mis-identified as belonging to an entity.

See mozilla/blok#104 (comment)

[groovecoder]

Also need to ensure there are no duplicate keys like

shavar-prod-lists/disconnect-entitylist.json

Lines 1135 to 1150 in b8105c1

	"Adsrevenue": {
	"properties": [
	"adsrevenue.net"
	],
	"resources": [
	"adsrevenue.net"
	]
	},
	"Adsrevenue": {
	"properties": [
	"adsnative.com"
	],
	"resources": [
	"adsnative.com"
	]
	},

.

[groovecoder]

Updated the title here since the first check (for duplicate domains) was done in 7387ebb