General refactoring

[dorianim]

Do general refactoring to make the code cleaner and easier to maintain

• Long functions are bad style. They should be avoided.
• One function should only have one purpose
• to-do:
  • Remove minimal layout, it causes too many problems and would have to be reimplemented cleanly
  • Handle the insertion of theme values into sytlesheets consistently #71
  • LinboBackend:
    • Split all QProcess stuff into a spereate class
    • Remove currentOS. It should not be handled in the backend
    • Split constructor
    • Split _executeCommand (now handled in LinboBackend)
    • Split _handleCommandFinished
    • Split cancelCurrentAction (it's good enough)
    • Add parameters to all signals to make getters obsolete
    • Move start, sync, reinstall to LinboOs
    • Move createImage and replaceImage to LinboOs
    • Combine root timeout timer and autostart timeout timer
    • Move some Stuff to LinboCmd to make the class smaller
  • LinboConfigReader
    • Split _loadStartConfiguration
    • Split _loadEnvironmentValues
    • Split _loadThemeConfiguration
    • Refactor all _parse functions (I did not find a better way to handle this)
  • LinboOs
    • Remove backend() function
  • LinboCheckbox
    • Replace + in strings with QString::asprintf
  • LinboComboBox
    • Replace + in strings with QString::asprintf
  • LinboDialog
    • Split constructor
    • Split paintEvent
    • Split setVisibleAnimated
    • Split resizeEvent
  • ModalOverlay
    • Split setVisibleAnimated
  • LinboLineEdit
    • Replace + in strings with QString::asprintf
  • LinboProgressbar
    • Split setIndeterminate
    • Split paintEvent
  • LinboPushButton
    • Split constructor
    • Split resizeEvent
    • Split setVisibleAnimated
    • Split paintEvent
  • LinboRadioButton
    • Replace + in strings with QString::asprintf
  • LinboTerminal
    • Replace + in strings with QString::asprintf
    • Split constructor
    • Split keyPressEvent
  • LinboTextBrowser
    • Split constructor
    • Replace + in strings with QString::asprintf
  • LinboImageCreationDialog
    • Split constructor
    • Split resizeEvent
    • Split _refreshPathAndDescription
  • LinboImageUploadDialog
    • Split constructor
    • Split resizeEvent
  • LinboRegisterDialog
    • Split constructor
    • Split resizeEvent
  • LinboUpdateCacheDialog
    • Split constructor
  • LinboClientInfo
    • Split constructor
    • Split resizeEvent
  • LinboMainPage
    • Split Constructor
    • Split _handleLinboStateChanged
    • Split eventFilter
  • LinboOsSelectButton
    • Split constructor
    • Split resizeEvent
    • Split _handleBackendStateChange
    • Split _updateActionButtonVisibility
  • LinboMainActions
    • Split constructor
    • Split _resizeAndPositionAllItems
    • Split _handleLinboStateChanged
  • LinboOsSelectionRow
    • Split _resizeAndPositionAllButtons
    • Split setMinimumSizeAnimated