Implement 1Password Vault Import

* Support importing 1Password vaults (.opvault folders) into KDBX database
* Entry attributes are filled based on section and field name
* Expiration dates are set for entries
* Entry URL's are set from a wider array of fields

src/gui/MainWindow.ui

@@ -200,6 +200,7 @@
       <string>&amp;Import</string>
      </property>
      <addaction name="actionImportKeePass1"/>
+     <addaction name="actionImportOpVault"/>
      <addaction name="actionImportCsv"/>
     </widget>
     <addaction name="actionDatabaseNew"/>
@@ -603,6 +604,14 @@
     <string>Import a KeePass 1 database</string>
    </property>
   </action>
+  <action name="actionImportOpVault">
+   <property name="text">
+    <string>1Password Vault...</string>
+   </property>
+   <property name="toolTip">
+    <string>Import a 1Password Vault</string>
+   </property>
+  </action>
   <action name="actionImportCsv">
    <property name="text">
     <string>CSV file...</string>