gschem: Line properties is non-modal

The dialog does not implement instant apply yet.
gschem: Make line property dialog box use instant apply
gschem: Prevent multiple selection from updating line properties
[WIP] gnetlist: Safer use of autogenerated "POWER" net names.

Two-pronged attack to make gnetlist's use of autogenerated "POWER"
net names less likely to cause a problem.

1) Add an initial space to the generated net names.  This will make it
   much much less likely that a collision with a user net name will
   occur.

2) When testing for autogenerated "POWER" netnames, use a regular
   expression that has to match the *whole* netname, rather than just
   looking for "POWER" appearing somewhere in the string.

Affects-bug: lp-1226246
[WIP] gnetlist: Warn users about clashes with "POWER" net names.

Generate a warning if a net name is found in input files that
conflicts with autogenerated "POWER" net names.

Affects-bug: lp-1226246