Help me develop an habit! I should be able to set up a constant goal.
Sometimes I don't wish to do more of something, I just wish to keep doing it everyday, like working on my thesis for at least 2 hours. I didn't find an easy way of setting up this goal on beeminder.

This is very much our fault that this isn’t clear but this is exactly what a “Do More” goal does. You tell it you want to spend 14 hours/week or however much and Beeminder holds you to that. You can increase or decrease the rate as you go.
If you literally want to do something every single day without exception indefinitely then you might prefer a Don’t-break-the-chain (aka Seinfeld hack) app — ideas at http://blog.beeminder.com/trackhack — but here’s why we think Beeminder is better:
The Seinfeld hack is great once you have a long chain built up. But once you do break the chain, all the motivation it provided bursts like a bubble. You’ve got to somehow motivate yourself to build up another long chain to not break. Until then you’re on a “one more day won’t matter” slippery slope of sloth.