Add/update preference screen icons

Defaults and language icons were missing, and graph/profile
icon was not readable.

All icons except "language.png" were taken from Google's
Material Design Icon pack which is distributed under Apache 2.0 license
(see https://github.com/google/material-design-icons)

Language icon is from http://languageicon.org site. If their
license isn't permissive enough, then we can switch to a language icon
from Material Design pack (globe).

Signed-off-by: Sergey Starosek <sergey.starosek@gmail.com>

1 files changed, 0 insertions, 0 deletions

diff --git a/icons/language.png b/icons/language.png
new file mode 100644
index 000000000..aec3433bf
--- /dev/null
+++ b/icons/language.png