Add change log for version code 538

Added:

- Add content descriptions to tabs in top bar

- Add accessibility action to toggle media sensitivity of posts in timelines

- Add accessibility actions to translate, download, share in media viewer

- Add a language indicator to focused status

Changed:

- Show placeholders while profile pictures are loading

- Update bottom navigation tab titles

- Improve accessibility of translated content

- Update list of tracking parameters used for "Remove UTM parameters"

- Use 'Tracking' instead of 'UTM'

- Improve accessibility in Manage timelines page

- Make the show/hide media button larger

- Update about page

Fixed:

- Bottom hashtags in bios disappear when "Highlight bottom hashtags" enabled

- "Use an alternative frontend" breaks Medium link

- Tapping publish button multiple times publishes status multiple times

- Alt text popup does not resize when swiping

- Video controls not visible in light theme