Manage delete at the beginning of paragraph

[openlowcode]

In RichTextArea, when delete / suppressed key is pressed at the beginning of the paragraph, the paragraph should be merged with the previous paragraph with the following rules:

• take the formatting of the last section of the previous paragraph for the first section of the current paragraph
• if formatting is allowed on current paragraph, then formatting is kept. Linked to Have clean management of two types of carriage returns in RichTextArea #72