Replace "Master Key" with "Database Credentials"

Definitions:
* Database Key - Cryptographic hash used to perform encrypt/decrypt of the database.

* Database Credentials - User facing term to refer to the collection of Password, Key File, and/or Hardware Key used to derive the Database Key.

Changes:
* Remove the term "master" and "key" from the user's lexicon and clarify  the code base based on the definitions above.
* Clean up wording in the UI to be clearer to the end user.

src/gui/DatabaseWidget.h

@@ -197,8 +197,8 @@ public slots:
     void switchToGroupEdit();
     void sortGroupsAsc();
     void sortGroupsDesc();
-    void switchToMasterKeyChange();
-    void switchToReports();
+    void switchToDatabaseSecurity();
+    void switchToDatabaseReports();
     void switchToDatabaseSettings();
     void switchToOpenDatabase();
     void switchToOpenDatabase(const QString& filePath);