ListSource has SourceContent

Now the sources for the transaction list panel have SourceContent.
Type of the SourceContent can be Temporary List (aka ImportStage) or
DatabaseFilter.

DatabaseFilter Type is basically a TransactionGetterStringFactory object
that passed to the ReloadActionListByListType function via the
global_view_info.Filter intermediate.

So when changing the source via InitiateTransactionPanel, it saves the
current filter (or temporary list) and set the Filter object to be the
one from global_view_info.SourcesTransactionLists.

Budget panel now sets the proper filter to the EventSource
DatabaseFilter in SourcesTransactionLists and initiates the Transaction
Panel with the EventSource argument.