The svg files produced by vector editors may end up containing a lot
of unused elements that increase their size without any impact on
quality. For example, this occurs when copy/pasting between images
such that unused effects or shadings simply clutter the files.
Removing these elements in some cases may reduce the size to one half
or one third of the original one, leaving unmodified the image quality.
I also tweaked some existing icons to make them look better at default size.
Moreover, some text was replaced with paths, because the required font may
not exist on a system and font substitution would take place, making the
icons look different on different systems.
