Tag edit: make it possible to use non-existing tags.

This is a workaround until #133 is properly solved. The tag list still
only autocompletes from a pre-defined list, but at least now you can
just set new tags as you wish.

src/components/Tasks/TaskEdit.tsx

@@ -456,6 +456,7 @@ class TaskEdit extends React.PureComponent<PropsType> {
 
           <Autocomplete
             style={styles.fullWidth}
+            freeSolo
             multiple
             options={TaskTags}
             value={this.state.tags}