Allow multiple tabs to be open

[daemontus]

Right now, we have working tabs that can be switched/closed/created.

Next step would be to make them more usable for "multitasking". In particular:

• The content area of each tab should have a small icon button somewhere in the corner which would "lock" it in place.
• When a tab is locked, opening some other tab will not hide the current one, but instead open the new tab next to the locked one.
• The tab opens either to the left or right depending on where the new tab is in the tab list/ordering.
• Ideally, it should be possible to lock multiple tabs like this, meaning I can have several "locked" tabs visible and one "selected" tab (in theory, the selected tab can be also locked) and they are all sorted based on the order in the tab list.
• When the lock button is clicked again, the tab disappears unless it is currently selected, in which case it stays visible until another tab is selected.
• Currently, there is no specific restriction on tab width/resizing, they just open next to each other with some sensible width distribution.
• When the window contracts such that the list of tabs overflows, the tab names disappear and only tab icons are visible (like browsers). The window can have minimal width to ensure tab icons are always visible.
• I think that with small window sizes, the locking mechanism will probably also not be available (or in general if too many tabs are locked; e.g. disable adding a new locked tab if current tab width is less than X). But we can look at this once the rest of the stuff is working.

For now, the list of tabs is static. For testing, we can use:

1. Regulations
2. Functions
3. Observations
4. Properties
5. Analysis
   Once the list is stable, I will find some icons for each one. Until then we can use some kind of placeholder.

[ivicic-petr]

apart from the last point addressed in #20

[daemontus]

Interaction between tabs and regulations editor: When a new tab opens, cytoscape should automatically move to preserve the center of the view (now the new tab renders "over" the existing content).