Project structure refactor:

- Change package name general_server to gateway
- Changing the structure of directories and packages
- Adding vendor to the project

internal/core/corestate/corestate.go

@@ -0,0 +1,22 @@
+package corestate
+
+type Stage string
+
+const (
+	StageNotReady Stage = "init"
+	StagePreInit  Stage = "pre-init"
+	StagePostInit Stage = "post-init"
+	StageReady    Stage = "event"
+)
+
+const (
+	StringsNone string = "none"
+)
+
+func NewCorestate(o *CoreState) *CoreState {
+	// TODO: create a convenient interface for creating a state
+	// if !utils.IsFullyInitialized(o) {
+	// 	return nil, fmt.Errorf("CoreState is not fully initialized")
+	// }
+	return o
+}