Configurable "mini" progress bar

I have enhanced the mini bar a bit for epubs in page modus.

Before:
Clicking on the mini bar toggled between pages/clock/off

Now:
You can select what you want to see in the mini bar: clock / pages / pages until next chapter / all three
With a new defaults.lua parameter DMINIBAR_ALL_AT_ONCE = true you can tell Koreader to show all three info (or some of them) at the same time. In this case a tap on the mini bar will just toggle between on and off.
With the following settings you can configure what exactly you want to see in the bar:
DMINIBAR_TIME = true
DMINIBAR_PAGES = true
DMINIBAR_NEXT_CHAPTER = true
If e.g. you you use 
DMINIBAR_ALL_AT_ONCE = false
DMINIBAR_TIME = true
DMINIBAR_PAGES = false
DMINIBAR_NEXT_CHAPTER = true
you will see the same behaviour as with the old system except that it will not show the xxx / yyy pages but the number of pages until the next chapter. It will toggle between this, the clock and off.
In case of no TOC the next chapter will point to the end of the book.

The functionality in scroll mode should be the same as before, but I can't make much sense out of this mode at all, so I am not sure if it really is the same as it always was. I suggest to remove the scroll mode for EPUBs completely.

Here's a screenshot how it looks with all 4 parameters turned to true:
![screenshot_2014-july-02_12h21 pam](https://cloud.githubusercontent.com/assets/7792441/3454743/5a92856c-01d5-11e4-8770-b5202f1f803c.png)
This reads as "it is 12:21, you are on page 1211 of 2422, in 5 pages the next chapter starts"