Add more attributes to capacitor components

[ubruhin]

SUMMARY

• Add attributes RATED_VOLTAGE (unipolar + bipolar) and DIELECTRIC (bipolar only).
• Also add these attributes to the component's default value to make them appear in schematics

Closes #137

DATASHEETS / REFERENCES

None

OPEN QUESTIONS / UNRESOLVED ISSUES

The schematic editor does not handle the new default value very well when adding new capacitors to the schematic, thus we should not merge this yet...

CHECKLIST

• I have read and followed the library conventions¹.
• For packages, I followed IPC7351C (see details in library conventions).
• For modified elements, I bumped their version number².
• I already used the new library elements in a design and verified their correctness (optional).
• I'm the copyright owner of the added content (i.e. the changes are made by myself, not copied/imported from somewhere else).
• I agree to publish all my changes under the CC0 Public Domain License³, allowing everyone to use and modify the content without any restrictions.

¹ Library Conventions: https://docs.librepcb.org/#libraryconventions
² Minor version bump if only metadata was modified (e.g. "0.1" -> "0.1.1"), major version bump if functional changes were made (e.g. "0.1" -> "0.2")
³ CC0 Public Domain License: https://en.wikipedia.org/wiki/CC0

[eduardosm]

The schematic editor does not handle the new default value very well when adding new capacitors to the schematic, thus we should not merge this yet...

Has this been fixed by LibrePCB/LibrePCB#1807?

[ubruhin]

Has this been fixed by LibrePCB/LibrePCB#1807?

I think so, thus I just updated this PR yesterday. I'll need to test, review and think about this again to decide if it is now ready to merge.

Also I think we should still wait a bit with merging this. There are still many people using LibrePCB 2.0. With this version, it would be bad to get the updated capacitors as the editor won't behave nicely with it. It's not a big deal for less used components, but the capacitor is one of the most used component so it would be very bad user experience.