Fix jshint warnings

Only the simple fixes to reduce risk, remaining cases to be analyzed:

	C:\vz>gulp jshint
	[gulp] Using gulpfile C:\vz\gulpfile.js
	[gulp] Starting 'jshint'...
	[gulp] Finished 'jshint' after 303 ms
	C:\vz\htdocs\frontend\javascripts\property.js: line 59, col 42, Use	'===' to compare with ''.

	1 error
	C:\vz\htdocs\frontend\javascripts\wui.js: line 517, col 20, Use '===' to compare with 'null'.
	C:\vz\htdocs\frontend\javascripts\wui.js: line 517, col 34, Use '===' to compare with 'null'.
	C:\vz\htdocs\frontend\javascripts\wui.js: line 522, col 15, Use '===' to compare with 'null'.