🎨 📝 Add validation for text fields on blocks

[njoroge-jane]

User stories

This issue depends on #316

As a user I would like to see a warning text to notify me that there are empty text field when I try to save my progress so that I will not be able to save my progress with empty text fields.

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Description

1. Have a check for empty fields.
2. On click of save have a pop up on detection of empty fields. 
3. The pop up should say 'Empty text field detected'.
4. Disable save button until all text fields are filled.

NOTE: This PR has a very limited description on designs intentionally as it requires some creative input.

[Dyesjr]

Working on this

[Beulah-Matt]

Working on this