Add new shower icon with solid design as "shower" and rename existing shower to "shower-outlined"

[1HitKilobyte]

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Most icons have a default solid/filled design and an alternative one that is outlined. There are a few that break from this convention and only have one version that is outlined such as the shower so I wanted to bring it up to convention so it is consistent with the others and makes both designs available.

Also, the sharp rim of the original tub looked a little hostile and the way the shower connects to the tub looks a bit too fragile and disconnected to me so I have tweaked these things to make them more friendly and secure.

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shower.zip