add sign-22.png to chrome manifest

this fixes the icon not being displayed in an inline encryption-frame of
the target web page.
fix logic which password dialog to open when signing

after a specific key is selected, the user is either in webmail mode
or external editor mode. Signing is nothing to do with decryption settings.
Now the test is correct and a popup is opened for webmail mode and the
password dialog is shown inline when in external editor mode.
add messageAdaptor for signDialog in firefox plugin

needed to sign messages in firefox
define openpgp and its util class in controller

needed for firefox to have openpgp object available, which is needed for
signing.
fix position of inline password dialog in editor

use the css from decryptPopup, so it is styled in the same way. Once css-files
are re-organized with less or sass, there can be a central file for styling
the password dialog.
make password dialog really modal in external editor

solution: hide modal editor dialog when pwd dialog shown

bootstrap behaves a little strange when two modal dialogs are open at the
same time. This should be refactored, later, but for now it looks as
intended. At least with all the nested iframes, it’s hard to get it right.
We should switch to a more template based approach, in the future.
remove encrypt dialog when password dialog is cancelled

assume that user want’s to start all over, when cancel is clicked.
Don‘t close the whole editor, since there might be unsaved text in it.
make EncryptFrame::removeDialog method more robust

only remove dialog if it is there. This method might be called in inline
edit mode, when there is now dialog available. In this case, only the
password dialog needs to be closed.

This prevents a crash when hitting 'cancel' in password dialog when
inline edit mode is active.
indicate loading state for signDialog ok button

when the password dialog is shown, the ok button should be disabled to
indicate the process that is going on. The ui waits for the key to get
unlocked.
Merge pull request #165 from johnyb/issue161

cleanup new plaintext signing feature