-Added currentCharacters method, a list counterpart of currentCharacter.
-Replaced the connection for currentItemChanged with itemSelectionChanged. This is to accommodate for the bulk-changes when multiple characters are selected. The currentItemChanged method is now not called with a connection, but from the handleCharacterSelectionChanged method. The latter is called with the itemSelectionChanged connection.
-If no valid characters are selected, the tabPersos widget is disabled. This obviously breaks the functionality of bulk-adding info to characters. This will have to be fixed by only disabling the parts of the tabPersos widget that should not be affected with multiple selection operations.
-Changed the selection mode to extended selection on the lstCharacters tree-view. This will not affect anything else other than the "detailed info" rows. Every other change to a character's descriptions, motivations and such only affect the last selected one.
-Made a method to get all the IDs of the selected characters.
-Added a character-info dialog UI. Originally, adding information worked by adding a placeholder and then changing it. Users never want to just add a placeholder without initialising the values. And the bulk-adding only works this way.
When creating a new character, sets an appropriate importance level.
* If a character is selected, the new character has the same importance level.
* If a top-level importance level is selected, the new character has that level
* Otherwise, the importance level is zero
