lot of changes, some new material

	modified:   frontmatter/abstract.tex
	modified:   frontmatter/foreword.tex
	modified:   mainmatter/chapter1.tex
	modified:   mainmatter/chapter3.tex
	new file:   resources/data/bridges_year_length.csv
	new file:   resources/images/basic_types.png
	new file:   resources/images/combination.png
	modified:   resources/resources.bib
	modified:   thesis.pdf
	modified:   thesis.tex