Add empty span for indicators to the snakview

Advantages of this solution:

• It works everywhere, in main snaks, qualifiers and references.
• It's independent from the skin and the planned redesign because it simply inlines smoothly with the value.

Disadvantages:

• It's the same class name for all indicator elements. You need a good CSS selector to target the correct element. Shouldn't be that hard: start with the statement GUID and then go deeper, possibly using ">" in the selector.
• The icons are not aligned. They are simply appended to the end of the values.
• There is no default padding. Each icon added to the empty element should come with a good padding that works in both LTR and RTL contexts, e.g. "padding: 0 0.5em".

Bug: T95403
Change-Id: I8250979fd105f2b9a3eb1c4ab188e3df15bfcd1a