Migrate notifier from portmaster-ui to cmds/notifier, remove some duplicated code, move assets to assets/data and add a small go package in assets to allow embedding icons

cmds/notifier/.gitignore

@@ -0,0 +1,34 @@
+# Compiled binaries
+notifier
+notifier.exe
+
+# Go vendor
+vendor
+
+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
+*.test
+*.prof
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out