Improve notifications logic

[leelokas]

Test-users have said that:

• 5 sec isn't enough to read the notifications
• there are too many notifications at once (for example: 4 when saving a new request)
• notifications should dissapear when url changes.

[lucyhilltop]

When user edits a request, the notification should also say 'send to confirmation' like it does, when creating new request

[leelokas]

Sick leave type requests do not need manager confirmation so the notification shouldn't say it was sent for confirmation. In addition, the alert currently displays "01/01/1970" as end date when the end date is missing.

[leelokas]

Alerts section is cleared when user changes between 'My vacations', 'Confirmation needed', 'Overview', 'Settings' or 'User Management' pages.