Investigate and implement script tag prevention

[szczz]

Description

During the 12-17 Platform meeting, we decided that we didn't want to remove the ability for tags to be included in text panels, despite the expectation for custom styles to be added from the advanced editor. There are greater benefits to allowing this than there are realistic risks from users choosing to add their styles this way.

However, we shouldn't allow things like scripts tags to be included as this is a security issue.

Investigate whether script tags can be injected in storylines products, and if so we need to implement a fix on the storylines side to properly strip these.

Related issues

ramp4-pcar4/storylines-editor#423