Simplify Eclipse setup.

Create .project files for all the Ecplipse projects
so they will all have project names and can
all be brought into Ecplipse together with a single
'File -> Import -> Android ->
Existing Android Code Into Workspace'.

(Not bothering to remove the .project exclusion from
all .gitignore files.  Once the .project files are
checked in, they will no longer be ignored.)

Modify the top .project file so that Eclipse knows
k9mail's dependence on it plugins, and thus will
build everything in the correct order.

With the latest Android SDK Rev. 22, the top .classpath file
needs modification or else K9 will not run (see parent commit 53fcdd18).
But the initial import of k9mail into Eclipse works more cleanly if the
.classpath file doesn't exist on import, in which case Eclipse creates it
automatically.  So rather than modify the .classpath file, remove it
from git and leave it untracked.

(For an existing Eclipse project, this commit will remove the file from
the working directory.  A corrected version can be restored with:
git checkout 53fcdd18 .classpath
git rm --cached .classpath)

Add .classpath to the top .gitignore, now that no
.classpath files are being tracked (with one exception,
see below).

Create a tests/.classpath so that Java can find the k9mail
project in order to build the k9mail-tests project.