divide by zero in instance creation

[Zekken01]

pasting

int main()
{
    int i = 1 / 0;
}

into the create an instance causes weird stuff

[peterix]

Instance naming needs some filtering:

• normalize whitespace to single spaces
• remove leading and trailing whitespace
• strip newlines and weird characters
• remove invisible unicode characters?
• forbid usage of !

For the on-disk name:

• strip/ASCII-ize unicode
• replace whitespace with _

[peterix]

Also see:
#847
#1105
#1674

[peterix]

This particular instance of this problem has been fixed in develop.