Editing a note turns insignificant newlines into explicit line breaks

Originally reported on Google Code with ID 2408

```
AnkiDroid v2.3.2/Android 4.3:

There is a field on some of my notes that contains HTML code as follows:

---

Headline

line 1

line 2

...

---

AnkiDroid displays this correctly.

But whenever I edit and save such a note, even if I do not touch that particular field,
each (insignificant) newline gets turned into another explicit line break, so I end
up with double-spaced output:

---

Headline

line 1

line 2

...

---

Expected behaviour:

1. AnkiDroid should not modify a field I did not edit.

2. AnkiDroid should not make insignificant whitespace read from existing content significant
when editing. For me, it would be acceptable to have it stripped if that helps (i.e.
to have the data above internally turned into

"

Headline

line 1
line2
..."

before being fed to the edit box); see 1. though.
```

Reported by `post@johannesrohrer.de` on 2014-11-17 11:56:10