## [SIEM] Overview page feedback
Implements feedback and fixes to the Overview page
### Overview (default theme)
### Overview (dark theme)
## Highlights
* The new order of widgets is Signals, Alerts, Events, Host Events, Network events, per https://github.com/elastic/siem-team/issues/494
* Changed the default `External alerts count` `Stack by` to `event.module` https://github.com/elastic/siem-team/issues/491
* Added `event.module` to the `Events count` histogram https://github.com/elastic/siem-team/issues/491
* Widget titles will no longer include the currently selected `Stack by option`. The widgets will use the same static title text that appears on the other pages (i.e.. `Signals count`, `External alerts count`, and `Events count`) https://github.com/elastic/siem-team/issues/491
* The `Signals count` includes a `Stack by` that defaults to `signal.rule.threat.tatic.name`
* Standardized on a 300px widget height for all histograms in the app (thanks @MichaelMarcialis for paring on this!)
* The `Open as duplicate timeline` action is `Recent timelines` is now only shown when hovering over a recent timeline
## Loading States
* The `Recent timelines` and `Security news` widgets now use the horizontal bar loading indicator
* The `Host events` and `Network events` widgets now use the horizontal bar loading indicator
* The `Host events` and `Network events` Showing _n_ events subtitles are now hidden on initial load
* The counts in the `Host events` and `Network events` Showing _n_ events subtitles are now hidden on initial load
* We no longer hide some histogram subtitles after initial load, to prevent shifting of content when a user makes a `Stack by` selection
## News Feed Error State
* Fixed an issue where the `Security news` header was hidden when an invalid URL is configured
* Added a space between the word `via` and the `SIEM advanced settings` link
* Removed the capital “N” from "News" in the error message
## Misc Visual Changes
* Fixed text truncation of the `Severity` column in the `Detections` page's `Signals` table
* Added the “showing” subtitle to the `Signals count` histogram on the Detections page
* Increased the `Stack by` histogram selector and the `View signals | alerts | events' buttons from 8 to 24px
* Tweaked the border rendering in the Overview `Host Events` and `Network events` widget headers
* Added 8px of spacing between the Overview `Host Events` and `Network events` widget accordion headers and their contents
* Fixed an issue where the `Host events` and `Networ events` widgets didn't render in ie11 https://github.com/elastic/siem-team/issues/499
## Non-Visual Fixes
* Removed an incorrect usage of `usememo`
* Removed the placeholder client-side username query from `x-pack/legacy/plugins/siem/public/components/recent_timelines/index.tsx`
* Updated the query of the Overview `Host events` widget to filter by "host.name exists"
* Updated the query of the Overview `Network events` widget to filter by "source.ip exists or destination.ip : exists"
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