Issue/516 crash special comments

[mzorz]

Fix

Fixes #516 by by re-setting the Editable after manipulating its spans, as commented in #516 (comment)
This PR proposes the use of a method within AztecEditor to make sure the Editable is reset.

It also fixes the case commented in #516 (comment)

Note: as a consequence of this change, I've observed the onMediaDeleted method for the DeleteMediaElementWatcher was called each time a new character/span was inserted right before the Caption, so that was also fixed in f43d5e2.

Test

on API 26/27:
CASE A:

1. start the demo app
2. tap on any special comment (More, Page) or HorizontalRuler icons on the Aztec toolbar
3. verify such character is inserted at the top of the demo content without crashing.

CASE B:

1. start the demo app
2. tap on the very left edge of the demo content image, trying to not touch the image itself, just to position the cursor at the very beginning.
3. enter any character on the keyboard, for example "a"
4. verify such character is inserted at the top of the demo content without crashing.

Also verify there's no changes in behavior for other API versions.

Review

@0nko

[0nko]

There is a slight problem. When I test Case B, all the headings (the style) in the app get removed.

[mzorz]

There is a slight problem. When I test Case B, all the headings (the style) in the app get removed.

Out of curiosity: have you tried this very same case B with the initial solution as proposed in #516 (comment)? Does the style go away as well?

[mzorz]

I think we can close this PR as the real solution will come in the form a fix from Google as stated here #516 (comment)