Weather: Fixed widget failing to load when using the Microsoft icon pack

Unfortunately, besides updating the code to work with Google's latest
changes, commit 2a1aad2 introduced a bug when using the Microsoft
icon pack that prevented the widget from loading. Thus, this commit:

* Fixes that (there was no need for `getElementById('wob_tci').children[0]`
apparently)
* Besides checking for blobs in `src`, it also checks for image names,
since `wob_tci` (main icon) still contains a URL, not a blob
* Fixes `wob_tci` to update with proper icon when interacting with the
widget, for example when selecting a day with a different forecast than
the current conditions
* Simplifies some logic, seems the widget works fine without it

Hopefully this fixes the widget properly.