fix: update wrong "goto" icon and add new icons (#27)

[silviowolf]

Summary

• wrong naming during export overwrote goto icon with arrow-right-down icon
• resolve naming issue in Sketch source
• update goto.svg
• add arrow-right-down.svg

[silviowolf]

@danielleroux: I have added a lot of new icons (Issues, SIMIT, etc.), please merge PR and release new icon font. Mörci!