Glade file taken from previous project, unchanged
Load glade file and quit pressing Exit button
Connect main gui panels
Some stuff done for billing concepts panel
Merge branch 'master' into gui
Merge branch 'master' into gui
addWorkingDays: today not count if non-working day
Show billing concepts info in tree view
Simpler show function for prices
More rename Guia -> Sepa
Better default GHC extensions
Apply haskell-mode-stylish-buffer to SepaDebits
Merge branch 'master' into gui

Conflicts:
	GuiaDirectDebits.hs

GuiaDirectDebits.hs -> SepaDebits.hs

Cabal file updated with package gtk3.
Rename payer -> debtor
Rename invoicing -> directDebit
Quit on main window destroy
Refactor billing concepts tree view code

Using glade for all user-visible texts, even tree view column labels.
Delete deprecated file
Billing concept columns, correctly aligned
Application state threaded down using ReaderT

App. state data types created with Lens interface.