View for scheduled/budgeted transactions

(from [47]) [#3] Started implementing a Schedule view. For now, it's read-only and has a lot of code duplication with ttable.

(from [48]) [#3] Fixed issues with Stop Date field edition. It's the first date field with a possibility of a None value, so the date field editor had to be improved to support that.

(from [49]) [#3] Implemented basic schedule edition in the sctable.

(from [50]) [#3] Disabled inline edition for the schedule table. After having tried to add a NSPopUpButtonCell as a cell for the Repeat Type column, it turns out that doing so messes greatly with the edition system. There doesn't seem to be an easy workaround so, for now, the schedule and budget tables edition will be modal only.

(from [52]) [#3] Added a first (barely) working schedule info panel.

(from [53]) [#3] Various improvements to schedule edition: fixed repeat_every_desc crash, refresh repeat_every_desc on load, start edition on return + double-click in sctable.

(from [54]) [#3] Fixed a crash when using up/down arrows on invalid date in date editor.

(from [56]) [#3] When changing the ref transaction of a schedule, reset spawn cache (so that the changes are actually reflected in the spawns right away).

(from [57]) [#3] It's now possible to add a new schedule through the sctable+scpanel.

(from [58]) [#3] Added support for deletion in sctable.

(from [59]) [#3] Removed support for scheduling in the tpanel (redundant with scpanel), which required changing around a lot of tests so the use scpanel rather than tpanel for schedule setup.

(from [60]) [#3] Refactoring: removed some code duplication in the scpanel.

(from [61]) [#3] Refactoring: removed a lot of duplicated code in panel code on the cocoa side.

(from [62]) [#3] Refactored the date increasing algorithm in schedules into a DateCounter iterator class, and made the exceptions of a schedule clear themselves upon repeat_type, repeat_every or start_date changes.

(from [64]) [#3] Added undo support for schedules.

(from [65]) [#3] Added keyboard shortcuts for selecting the schedule view.

(from [66]) [#3] Added the "Make Schedule from Selected" feature.

(from [67]) [#3] Refactoring: Moved panel code around so more GUI control is given to the py side (pre_load, post_load, pre_save).

(from [68]) [#3] Refactoring: I had forgotten to refactor the new() method of the schedule panel in my last commit.

(from [69]) [#3] The Repeat Type column in the sctable now has the same value as in the scpanel (rather than just the rtype identifier).

(from [73]) [#3] Began implementing the budget table.

(from [74]) [#3] Added the budget info panel.