Overview page and electronic structure handling improvements

• Now placeholders are always shown while loading the data that is indicated to be present in searchable_quantities. Also improved the detection of searchable_quantities within processing for electronic_dos, electronic_band_structure, phonon_dos, phonon_band_structure (this will show up only after re-processing).
• Added correct shifts in the BS/DOS plots shown in the GUI, added a horizontal line + legend that indicates the highest occupied energy in the plots (example). If normalization cannot be detected, a small warning icon will be shown with a tooltip (example).
• Fixed issue with plotting spin-polarized band structures and band structures with discontinuous segments.
• Modified the geometry optimization card to only show the energy convergence plot. The energy convergence now shows the absolute energy change (+convergence threshold if available) on a separate logarithmic y-axis (example) (related to #517 (closed))
• Fixed incorrect band/dos shifts in exciting and FHI-aims (related to #521 (closed))
• Fixed GW parsing in exciting (#323 (closed))

There are still examples where the placeholders will not show up until reprocessing is done. E.g. here there is no electronic_dos in searchable quantities because of old processing.

@mscheidg: When you have the time, can you check that these changes are OK? When this is merged to v0.10.3, I could also rebase dev-newentry to v0.10.3.