0.1 update, make the stop container code more robust and fix some bugs, update the about screen for version 0.1

tests/test_operation_state.cpp

@@ -0,0 +1,19 @@
+#include "operation_state.hpp"
+
+#include <cassert>
+#include <iostream>
+
+int main() {
+    OperationState operation;
+    assert(!operation.busy());
+
+    operation.begin("Stopping container", "Please wait...");
+    assert(operation.busy());
+    assert(operation.title() == "Stopping container");
+    assert(operation.message() == "Please wait...");
+
+    operation.complete("Container stopped.");
+    assert(!operation.busy());
+    assert(operation.result() == "Container stopped.");
+    std::cout << "Operation state tests passed\n";
+}