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/DatabaseTabWidget.cpp

@@ -476,17 +476,17 @@ bool DatabaseTabWidget::warnOnExport()
     return ans == MessageBox::Yes;
 }
 
-void DatabaseTabWidget::changeMasterKey()
+void DatabaseTabWidget::showDatabaseSecurity()
 {
-    currentDatabaseWidget()->switchToMasterKeyChange();
+    currentDatabaseWidget()->switchToDatabaseSecurity();
 }
 
-void DatabaseTabWidget::changeReports()
+void DatabaseTabWidget::showDatabaseReports()
 {
-    currentDatabaseWidget()->switchToReports();
+    currentDatabaseWidget()->switchToDatabaseReports();
 }
 
-void DatabaseTabWidget::changeDatabaseSettings()
+void DatabaseTabWidget::showDatabaseSettings()
 {
     currentDatabaseWidget()->switchToDatabaseSettings();
 }