Fix memory leaks

Reduce definitely lost

Before:

  ==5836== LEAK SUMMARY:
  ==5836==    definitely lost: 99,435 bytes in 549 blocks
  ==5836==    indirectly lost: 101,154,375 bytes in 881,013 blocks
  ==5836==      possibly lost: 173,778 bytes in 1,678 blocks
  ==5836==    still reachable: 20,033,236 bytes in 82,359 blocks

After:

  ==7294== LEAK SUMMARY:
  ==7294==    definitely lost: 93,155 bytes in 498 blocks
  ==7294==    indirectly lost: 88,383,626 bytes in 772,926 blocks
  ==7294==      possibly lost: 71,891 bytes in 902 blocks
  ==7294==    still reachable: 20,016,025 bytes in 82,184 blocks
  ==7294==                       of which reachable via heuristic:

src/virtualkeyboardcustom.h

@@ -45,6 +45,7 @@ class CustomKeyboard : public I18nKeyboard {
         label_ = loader_->label();
         languageCode_ = std::string(loader_->languageCode());
     }
+    ~CustomKeyboard() { delete loader_; }
     int mode() { return mode_; }
     void switchMode();
     bool isAdditionalMarkOn() const { return isAdditionalMarkOn_; }

src/virtualkeyboardlayout.h

@@ -35,6 +35,13 @@ class KeyboardLayout {
         }
     }
 
+    ~KeyboardLayout() {
+        keys_.clear();
+        stateLabels_.clear();
+        modeLabels_.clear();
+        modeActions_.clear();
+        modeOffsets_.clear();
+    }
     // Keyboard metadata
     const char *label() { return label_; }
     const char *languageCode() { return languageCode_; }