Multiple selections

[honzaap]

Allow user to select multiple components. That can be done by:

• Pressing and holding LMB and selecting components (like in windows)
• Holding CTRL and clicking on components (also just like in windows...) A lot of changes will be made, especially to selection service since the app in not made for this right now. Moving the board will now be done by either RMB or MMB (or both)

Once multiple components are selected, you can move them together and they will remain the same distance between them. Since properties can change, only the "General" section will be present in options.

[honzaap]

Somewhat done, need some minor tweaks and also store connections of copied components (Issue #31)