Display image inside of indicator

[ErikReider]

Example: swaylock --indicator-image /var/lib/AccountsService/icons/erikreider

fade-in=0.2
image=~/.cache/wallpaper

ignore-empty-password

indicator
indicator-caps-lock
indicator-radius=60
indicator-thickness=5

effect-blur=12x12
effect-vignette=0.5:0.5

line-color=00000000
line-clear-color=00000000
line-caps-lock-color=00000000
line-ver-color=00000000
line-wrong-color=00000000

ring-color=00000033
ring-caps-lock-color=5500A3FF
ring-wrong-color=FF0000FF

separator-color=00000000

text-color=00000000
text-clear-color=00000000
text-clear-color=00000000
text-wrong-color=00000000
text-ver-color=00000000
text-caps-lock-color=00000000

inside-color=00000000
inside-clear-color=00000000
inside-caps-lock-color=00000000
inside-ver-color=00000000
inside-wrong-color=00000000

Fixes #68