Extract DDMS PreferenceStore. Do not merge.

Splits DDMS PreferenceStore management in
a separate class and add the methods we need
for ADT first-time wizard.

Various pieces of DDMS access the pref store
via the PrefsDialog. This could use a cleanup
eventually later.

(cherry picked from commit f7bc23a0f19d2e3371cbea41d4cf8a1081c9d2d8)

Change-Id: Iac37f970e69b7d74d9dd15120b838bcc47ba1caa
6 files changed