Avoid auto-downloading update
### Description

When there's a new version available, Kactus automatically downloads and installs that version. 
This is bad behaviour. Please at least ask the user if he/she want's to update and/or download the update now.
In the current situation (where 0.2.4 throws errors and 0.2.3 does not) this is especially bad, but also when you're on the go (maybe even using a limited data-plan)

### Version

**Kactus version:**0.2.x

**OS version:** MacOS 10.12.6

**Expected behavior:** Ask the user if he/she wants to download the update
**Actual behavior:** Update is downloaded without asking
**Reproduces how often:** 100
