Speed up the launch when there are lots of entries

[yyoon]

One user reported that Journaley launches very slow, and it appears that the reason for this is having lots of journal entries in the database (~2000).

As it stands, the main window of Journaley launches only after reading the entire journal database, which is not very efficient. We'll have to implement some background loading technique similar to #22.

[sguergachi]

maybe work on this can be coupled with #23 to make speed of the entire app a focus.